Backup

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      <text bytes="103" sha1="eq6ehncgsrzvzajbmbtrabsug7n2g45" xml:space="preserve">* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]</text>
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      <text bytes="156" sha1="kgizfmrofvq8ir9ewmoz07p699vjsgr" xml:space="preserve">* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]</text>
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        <username>Dave Braunschweig</username>
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      <comment>Introduction</comment>
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      <text bytes="1282" sha1="6zyi5tsxus3nd001v4eg04xjbqenfxe" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan. One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <comment>(DRP)</comment>
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      <text bytes="1288" sha1="mcgcqxo48w25g9vte0xq3343myy9qcx" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <text bytes="1515" sha1="e93562xxcw8c0nq25lelr4ebjok1haa" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <comment>/* Commercial Backup products */ == Activities == # Read about [[w:NDMP]]</comment>
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      <text bytes="1557" sha1="1b8li9c4ula2a9lgyyq2l85y88siks6" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== Activities ==
# Read about [[w:NDMP]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <comment>/* Activities */</comment>
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      <text bytes="1591" sha1="b3moo9hc6nncizng19e0i54gz168ekd" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <text bytes="1609" sha1="klrzl9peosxsm1quda96hzwc0tvra68" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <text bytes="1621" sha1="mxuqd8nl6r6bek18t164u8eysd9tyrv" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <minor/>
      <comment>Dave Braunschweig moved page [[Backup]] to [[Draft:Backup]] without leaving a redirect: Moving to draft space</comment>
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      <text bytes="1621" sha1="mxuqd8nl6r6bek18t164u8eysd9tyrv" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;


== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].


== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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        <username>Marcus Alanius</username>
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      <comment>/* File system structure image */ as fallback solution</comment>
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      <text bytes="2542" sha1="9plz7usmxn4h1pzpe2hgoxqi80qqy2u" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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        <username>Meadeyamo</username>
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      <comment>Types of data storage</comment>
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      <text bytes="2809" sha1="1rnawj3cngfwu8zpmkq3o2sb1r5e336" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and oinear tape have the most reliability for archival storage. The latter two are not vulnerable to mechanical failure due to modularity.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <text bytes="3145" sha1="j31vrofcznmv7jukxjquhjzbveb24fy" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and oinear tape have the most reliability for archival storage. The latter two are not vulnerable to mechanical failure due to modularity.

Flash memory (solid state drives, USB sticks, SD cards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data loses charge over time. Those may be suitable for secondary backups however.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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        <username>Meadeyamo</username>
        <id>2910582</id>
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      <text bytes="3514" sha1="p4yavf90w2k2a0q1y96sgtn6m9igebw" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and oinear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure due to modularity.

Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data loses charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however.

Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user. However, Cloud storage can act as a temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <text bytes="3514" sha1="al293a8v88rvrpaolp2rbxiufmd80ph" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure due to modularity.

Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data loses charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however.

Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user. However, Cloud storage can act as a temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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        <id>2910582</id>
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      <text bytes="3909" sha1="0grf4sv949v6x1m2a55t1ykc3qflspa" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of correctible errors suggests sooner data corruption.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data loses charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user, and access requires internet connection. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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      <comment>/* Magnetic and optical */ Errornous grammar fix; more elaborate</comment>
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      <text bytes="3949" sha1="m1y9bychj2u1waetvtiitby302tvvdq" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data loses charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user, and access requires internet connection. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
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    <revision>
      <id>2253316</id>
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      <timestamp>2021-01-26T10:15:27Z</timestamp>
      <contributor>
        <ip>84.147.35.183</ip>
      </contributor>
      <comment>/* Flash storage */ + While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.</comment>
      <origin>2253316</origin>
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      <text bytes="4085" sha1="j041h0aqgzvtb76akd2o41ni3kes3tb" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user, and access requires internet connection. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
      <sha1>j041h0aqgzvtb76akd2o41ni3kes3tb</sha1>
    </revision>
    <revision>
      <id>2253328</id>
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      <timestamp>2021-01-26T11:43:22Z</timestamp>
      <contributor>
        <ip>84.147.35.183</ip>
      </contributor>
      <comment>/* Flash storage */ And cited</comment>
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      <text bytes="4350" sha1="jc2rvvsbil9qnn8arewtbsjx3zswb2p" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user, and access requires internet connection. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]</text>
      <sha1>jc2rvvsbil9qnn8arewtbsjx3zswb2p</sha1>
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    <revision>
      <id>2268508</id>
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      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <comment>Added to categories</comment>
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      <format>text/x-wiki</format>
      <text bytes="4386" sha1="7n3gajd9msh626jpt9yhcyra0t2d4pf" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, and technical difficulties are not predictable to a end user, and access requires internet connection. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]]
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>7n3gajd9msh626jpt9yhcyra0t2d4pf</sha1>
    </revision>
    <revision>
      <id>2281511</id>
      <parentid>2268508</parentid>
      <timestamp>2021-05-01T14:59:23Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>As with any online service, cloud storage has a slight but noteworthy possibility of erroneous account termination.</comment>
      <origin>2281511</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="4543" sha1="3zqehvp0nebnjwi4k9ksjdx4gvqouf0" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to a end user, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>3zqehvp0nebnjwi4k9ksjdx4gvqouf0</sha1>
    </revision>
    <revision>
      <id>2281512</id>
      <parentid>2281511</parentid>
      <timestamp>2021-05-01T15:01:22Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <minor/>
      <comment>plural more suitable here</comment>
      <origin>2281512</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="4542" sha1="eajjgbvkdh6v2h7h2u2y082som8aclb" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be puzzled together.

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>eajjgbvkdh6v2h7h2u2y082som8aclb</sha1>
    </revision>
    <revision>
      <id>2281514</id>
      <parentid>2281512</parentid>
      <timestamp>2021-05-01T15:21:29Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>About compressed archives</comment>
      <origin>2281514</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="5468" sha1="4oyz3sfixa5aqdie6wz2angl8x30zt5" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity. 

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

To get an idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes. This experiment might not be as effective on a JPEG image, as its compression algorithm is more robust against damage.

Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds and making it vulnerable to damage.

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>4oyz3sfixa5aqdie6wz2angl8x30zt5</sha1>
    </revision>
    <revision>
      <id>2281532</id>
      <parentid>2281514</parentid>
      <timestamp>2021-05-01T19:47:03Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>Section order changed: More essential information further up; more details on storage media.</comment>
      <origin>2281532</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="5689" sha1="8roax4s42dxrmelcxjlppsbf0cv3wt4" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

To get an idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes. This experiment might not be as effective on a JPEG image, as its compression algorithm is more robust against damage.

Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds and making it vulnerable to damage.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>8roax4s42dxrmelcxjlppsbf0cv3wt4</sha1>
    </revision>
    <revision>
      <id>2281534</id>
      <parentid>2281532</parentid>
      <timestamp>2021-05-01T20:00:38Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <minor/>
      <comment>Marcus Alanius moved page [[Draft:Backup]] to [[Backup]]: The resource appears mature now, but is still open to further improvement.</comment>
      <origin>2281532</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="5689" sha1="8roax4s42dxrmelcxjlppsbf0cv3wt4" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

To get an idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes. This experiment might not be as effective on a JPEG image, as its compression algorithm is more robust against damage.

Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds and making it vulnerable to damage.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2281543</id>
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      <contributor>
        <username>Marcus Alanius</username>
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      <text bytes="6215" sha1="01b7xv8zo3mjv454cpffpm97ctvbdlh" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

To get an idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes. This experiment might not be as effective on a JPEG image, as its compression algorithm is more robust against damage.

Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds and making it vulnerable to damage.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2281545</id>
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      <timestamp>2021-05-01T21:17:49Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="6761" sha1="2cgf1omrlwnh41alp1mtv2l7l20l0h0" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP). The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds and making it vulnerable to damage.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2281555</id>
      <parentid>2281545</parentid>
      <timestamp>2021-05-01T21:27:02Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="7191" sha1="fyjgm3xeigmzp0rqfwuarfkhpo92v0s" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, while digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2281611</id>
      <parentid>2281555</parentid>
      <timestamp>2021-05-01T23:53:40Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <comment>/* Efficiency */Handling of many small files</comment>
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      <text bytes="7709" sha1="fefcys7f1zsytn69v49uoyyt9yqz4x5" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2281983</id>
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      <timestamp>2021-05-03T23:31:37Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
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      <text bytes="7747" sha1="18nz6mlx63enf8nbmqny5i89b5j156l" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== File system structure image ==
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2282155</id>
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      <text bytes="8178" sha1="3dsw7kni32pb4jw2wacjvlrwccpsc19" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2282156</id>
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      <text bytes="8290" sha1="gu9tijx45iygg9y3utzk6tc4pgd1ob0" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2282292</id>
      <parentid>2282156</parentid>
      <timestamp>2021-05-05T14:41:54Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="8607" sha1="5ncgwg3tyu6h70p2usbaa9lal8g2xih" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for secondary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a secondary, temporary off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="8619" sha1="4yxd1li2as8zxgjp4gsoxvsumhwhwmk" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2293490</id>
      <parentid>2293342</parentid>
      <timestamp>2021-06-30T10:23:33Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <comment>/* Web browsing */ distinctions between extensions for session exports</comment>
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      <text bytes="9358" sha1="0jatuqmrzukf5p65srvewnzkect73ai" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
Compressed archives may be used where efficient, but with the knowledge that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2293492</id>
      <parentid>2293490</parentid>
      <timestamp>2021-06-30T10:42:13Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>/* Compressed archives */ compression ratios and damage recovery</comment>
      <origin>2293492</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="10330" sha1="ehc97jbm586b36stneg9z5khsjz9iav" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve a compression ratio of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>ehc97jbm586b36stneg9z5khsjz9iav</sha1>
    </revision>
    <revision>
      <id>2293496</id>
      <parentid>2293492</parentid>
      <timestamp>2021-06-30T11:20:19Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>Added section: /* Other tips */:  If you are unable to physically locate a data storage device which contains a backup […]</comment>
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      <text bytes="10759" sha1="4w9a640ze1xb2zxxm4eth8p50lfrkhq" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="10891" sha1="gfalojjry9o10hmlzo9ydhvak3zrk6h" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    <revision>
      <id>2294543</id>
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        <username>Marcus Alanius</username>
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      <text bytes="12954" sha1="a2dffw3qkctlimsie4k17fxn79wzlto" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as [https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache] prevent loss of form data by backing it up automatically.

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months.

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the &lt;code&gt;places.sqlite&lt;/code&gt; live database file located in Firefox's profile folder, or exporting it into your download folder using a Google Chrome/Chromium extension like "''[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*]''". 

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="13691" sha1="jpmmdtkmk8curfoek286g7toeui231c" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2294697</id>
      <parentid>2294545</parentid>
      <timestamp>2021-07-07T11:07:20Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>/* Magnification of damage */ redundancy on same device</comment>
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      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="14079" sha1="px72y6vax3s9buaz16tyelllkpxew7l" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive (depending on compression method) useless. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>px72y6vax3s9buaz16tyelllkpxew7l</sha1>
    </revision>
    <revision>
      <id>2295280</id>
      <parentid>2294697</parentid>
      <timestamp>2021-07-10T12:55:57Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <comment>Mentioned solid compression.</comment>
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      <format>text/x-wiki</format>
      <text bytes="14233" sha1="qu3kns69vj5nwdas4v9hxnou73mzk5d" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>qu3kns69vj5nwdas4v9hxnou73mzk5d</sha1>
    </revision>
    <revision>
      <id>2303558</id>
      <parentid>2295280</parentid>
      <timestamp>2021-08-07T08:38:49Z</timestamp>
      <contributor>
        <username>Bricomsci</username>
        <id>2921477</id>
      </contributor>
      <comment>/* Other tips */ keeping track of manual backups</comment>
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      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="14493" sha1="738r52r42ki675cxj1hhd7pci97lu33" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>738r52r42ki675cxj1hhd7pci97lu33</sha1>
    </revision>
    <revision>
      <id>2304084</id>
      <parentid>2303558</parentid>
      <timestamp>2021-08-10T01:47:56Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>/* Flash storage */ mirroring</comment>
      <origin>2304084</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="15179" sha1="r8jvglj2z1or4coh83a6n79spqvaaai" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <id>2304085</id>
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      <timestamp>2021-08-10T01:57:38Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="15453" sha1="rfvmvznlj2brilx0p72kha6k0il00kn" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>rfvmvznlj2brilx0p72kha6k0il00kn</sha1>
    </revision>
    <revision>
      <id>2304086</id>
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      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="15613" sha1="8jaxptixuawdck66r2h1c00h3yt7nqp" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>8jaxptixuawdck66r2h1c00h3yt7nqp</sha1>
    </revision>
    <revision>
      <id>2304087</id>
      <parentid>2304086</parentid>
      <timestamp>2021-08-10T02:10:34Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <comment>/* Other areas */ Paper – also worth a mention.</comment>
      <origin>2304087</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="16991" sha1="dz949cauoi2g8fpf7suey6x72hz64b4" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>dz949cauoi2g8fpf7suey6x72hz64b4</sha1>
    </revision>
    <revision>
      <id>2304149</id>
      <parentid>2304087</parentid>
      <timestamp>2021-08-10T10:37:17Z</timestamp>
      <contributor>
        <username>Bricomsci</username>
        <id>2921477</id>
      </contributor>
      <comment>/* Other tips */ untrustworthy and second-hand data storage</comment>
      <origin>2304149</origin>
      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="17144" sha1="8art1x5qag3ovyxn0045thqc4gc0wj0" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression in an archive format such as ''Zip'', ''RAR'', and ''7z'' would not make much of a difference, while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <id>2306320</id>
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        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="17150" sha1="on63789txrizp2qx5xjszqnruxi2jio" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>on63789txrizp2qx5xjszqnruxi2jio</sha1>
    </revision>
    <revision>
      <id>2308664</id>
      <parentid>2306320</parentid>
      <timestamp>2021-08-23T03:03:57Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
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      <text bytes="17389" sha1="6mffav999tq5ptm0s3q1tv42pbzeq8d" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File Management/Directory structure|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>6mffav999tq5ptm0s3q1tv42pbzeq8d</sha1>
    </revision>
    <revision>
      <id>2308666</id>
      <parentid>2308664</parentid>
      <timestamp>2021-08-23T03:05:20Z</timestamp>
      <contributor>
        <username>Marcus Alanius</username>
        <id>2909170</id>
      </contributor>
      <minor/>
      <comment>/* Other tips */ [[File management/Directory structures|wiki link]] corrected</comment>
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      <text bytes="17390" sha1="p02q416fwly0blf5i6fxaqwjbe7ray0" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>p02q416fwly0blf5i6fxaqwjbe7ray0</sha1>
    </revision>
    <revision>
      <id>2314706</id>
      <parentid>2308666</parentid>
      <timestamp>2021-09-01T15:01:34Z</timestamp>
      <contributor>
        <username>MrTopali</username>
        <id>2926624</id>
      </contributor>
      <comment>/* Magnetic and optical */ Added more tips for long-term storage.</comment>
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      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="17695" sha1="or4d7men63b689p9xuknwovfmxoh1nt" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <id>2314707</id>
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        <username>MrTopali</username>
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      <text bytes="18017" sha1="rt9a0qft9fvehutsrky29rc3kkmndd6" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2314708</id>
      <parentid>2314707</parentid>
      <timestamp>2021-09-01T15:23:36Z</timestamp>
      <contributor>
        <username>MrTopali</username>
        <id>2926624</id>
      </contributor>
      <comment>Mentioned "Murphy's Law"</comment>
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      <text bytes="18171" sha1="6wgrz0cvce52n33b4nvbgbysvcgbcn3" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". Any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>MrTopali</username>
        <id>2926624</id>
      </contributor>
      <comment>Avoid humidity during HDD operation.</comment>
      <origin>2314709</origin>
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      <text bytes="18374" sha1="ljq799c3i4sgqmk7vkm6cfi1ojg5now" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided '''during''' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <id>2314713</id>
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      <timestamp>2021-09-01T15:38:48Z</timestamp>
      <contributor>
        <username>MrTopali</username>
        <id>2926624</id>
      </contributor>
      <comment>/* Magnetic and optical */ Added a source.</comment>
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      <model>wikitext</model>
      <format>text/x-wiki</format>
      <text bytes="18571" sha1="7onrlxwkd1eidf6ktxyzpxrajx5sz77" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided '''during''' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <comment>/* Magnetic and optical */ Describing retrieval from optical disc drives.</comment>
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      <text bytes="18862" sha1="183tw5yzsbrth2rjm8iq5rpc9wvtuep" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided '''during''' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every 

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most robust and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
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      <text bytes="18941" sha1="kdz9kb3h3pkh3en49uxa2xw5pnnca45" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided '''during''' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every 

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage, and deteriorates throughout weardown caused by repeated program/erase cycles. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users, and access requires internet connection. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="18977" sha1="brzhojkiyke2wxp44cmvchw9vo6mqvy" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Optical media is best stored in a dry and cold environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided '''during''' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every 

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage, and deteriorates throughout weardown caused by repeated program/erase cycles. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="19421" sha1="6m9ojupe0o8zdk4ocduzldkqlo58qvg" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may lose strength over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every . A slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage, and deteriorates throughout weardown caused by repeated program/erase cycles. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="19617" sha1="28xqwawqu2kzwk400ymjwjm86v0l664" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may fade over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on tapes also fades over time. A slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and may not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. The retention duration tends to be shorter for higher-density storage, and deteriorates throughout weardown caused by repeated program/erase cycles. Those are suitable for supplementary backups and short-term storage however. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="20290" sha1="5n5mgq3chnysiqtx8osl756rx9lhbdp" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may fade over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on tapes also fades over time. A slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter for higher-density storage, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. 

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="20480" sha1="32wr827qnokefywckcuhoetv3bgd98v" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may fade over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on tapes also fades over time. A slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans, technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="20672" sha1="h4af92jgg7i0hjv7ivgg03d7v2c35pl" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields may fade over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on tapes also fades over time. A slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="21015" sha1="e7wk4eitgdqhn7vke9ljndmdsedf9ov" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt;

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
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      <text bytes="21190" sha1="qmcg67qbdcces2t9or6thdyrs8nobp5" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="21896" sha1="c2e8o0hr16t4vzr9b2gwh60a450bq8p" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive natural disasters such as a flood or the marginial possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components.

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Bricomsci</username>
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      <text bytes="22007" sha1="hwpqbl8bq2dmsfbtgh00wqgoara6v2t" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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    </revision>
    <revision>
      <id>2315492</id>
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      <text bytes="22374" sha1="my4kax3hhnxu1ri1jxt6xcgth45r3bq" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to the archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless, The scope of the damage depends on compression method, where [[w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations, though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors with damaged data as null bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Marcus Alanius</username>
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      <text bytes="22617" sha1="nhaje5yzttubuvqv7951rdajroj5kt3" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="22653" sha1="naas2xo4e2d9lg8zcatz911xiqiva31" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
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      <text bytes="22802" sha1="tmddxfeqi0et3h0mf6hz5d78p54st10" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text=If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.}}
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text=Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.}}
* {{Visible anchor|lastbackup|text=Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.}}
* {{Visible anchor|reputableBrands|text=Data storage not from reputable brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.}}

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="22922" sha1="9bwx4109zh3i4pl684trnonsj3o8nc7" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Lapisgaming</username>
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      <comment>+ warning about proprietary formats</comment>
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      <text bytes="23252" sha1="mb1sg7qxkt3ncvpbf7sbd1n69vkltoh" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:en:vendor lock-in|vendor lock-in]].

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="23251" sha1="al18rv24n133da9kuuf8fqu5lco90il" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]].

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
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      <text bytes="23631" sha1="kkhwudsfhe72kn91hwvsojvgzjl6dgd" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]].

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <contributor>
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      <text bytes="24163" sha1="staaik2k991fzyk4k9s48p9dckiphlz" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud storage is technically not controllable by the end user. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well. However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="24988" sha1="mfnapog5ff3ve9js4z0tkwx1ddeyro7" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. As such, it is just an extension and not a substitute to local data storage. Services might have varying retention spans and inactivity policies&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="26432" sha1="k6bsk0kuvxsj9dagnlw5dmuxhqnf1jn" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Cloud storage ===
Cloud data storage it is just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. As with any online service, the slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
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      <text bytes="26445" sha1="o34e5y7ub94vk5et8x9w5vc7ecpgt29" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>o34e5y7ub94vk5et8x9w5vc7ecpgt29</sha1>
    </revision>
    <revision>
      <id>2422324</id>
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      <timestamp>2022-09-01T01:01:41Z</timestamp>
      <contributor>
        <username>TechActus</username>
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      <comment>About lock-in of data.</comment>
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      <text bytes="28752" sha1="efpx17oz0z9x1iccdfwpkdmxhwyg2x7" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Data lock-in occurs when digital data is present somewhere, but not accessible, and if accessible, then not portable. Examples of such include: 

* Because HD-DVD did not succeed in the market, or manage to co-exist with BluRay (see ''High-definition optical disc format war''), it is possible that some people own recordable HD-DVD's but no optical drive that reads them. A blu-ray drive could technically read HD-DVD's, but optical drive manufacturers see no need in implementing HD-DVD support.
* Samsung S Browser for Android: The “saved pages” are stored in the directory &lt;code&gt;/data/com.sec.android.app.sbrowser/&lt;/code&gt;. If the device bootloader is locked (as by default), the originally saved pages are trapped. It is possible to access the source code by prepending &lt;code&gt;view-source:&lt;/code&gt; to the displayed resource locator, and then copy it to the clipboard. But this would have to be done once at a time for each saved page. In addition, media such as images have to be exctracted individually by opening each inside “S Browser” and saving them individually.
** Google Chrome handles saving pages in a superior way: It stores them as an MHTML document in the download folder of the user storage (i.e. &lt;code&gt;/storage/emulated/0/download/&lt;/code&gt; or &lt;code&gt;/sdcard/download&lt;/code&gt; ), where they can be backed up and sent to other devices.
** The same does apply to other system applications that hold personal data users might want to back up.
** Bootloader unlocking leads to wipe, which equals a hard reset, since all user data is erased.
* The session of Google Chrome for Android and “Samsung S Browser” is also trapped inside their respective &lt;code&gt;/data/&lt;/code&gt; folders. The browsers deny browsing their own &lt;code&gt;/data/&lt;/code&gt; folders.
* Some earlier  digital voice recorders and the recorder of the answering machine of some home telephone units have no interface for to transfer the data to a computer or flash memory. The only non-forensic method of preserving the audio data is to play it back and record it over the air, using an external audio recorder, which causes a significant loss of audio quality.
* When the bootloader of an Android mobile device is locked, it is impossible to capture an exact disk image without using forensic tools.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="27897" sha1="sc95a5c0hzhgvakzy2jwml40omx39mu" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;https://beepb00p.xyz/exports.html&lt;/ref&gt;


== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which did not succeed in the market. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A blu-ray drive could technically read HD-DVD's, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="28181" sha1="jfh4abvh6yv4evtgja9vs6tr7widrmw" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which did not succeed in the market. Unlike DVD plus and minus formats, HD-DVD [[:w:https://en.wikipedia.org/wiki/High_definition_optical_disc_format_war|could not successfully co-exist with its competing format]], the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="28153" sha1="eeip1homptgsn5tligipkf002ixai07" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format]], the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="28151" sha1="fkn18qfgva4jdesypqh6rh8rgc8580s" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <comment>summary of [[Backup/Causes of data loss]]</comment>
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      <text bytes="28432" sha1="kf6v53vcf7rjsc2lg9mswz20t42kou6" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data lose charge over time. They are suitable for supplementary backups and short-term storage however. The main use of flash storage is for portable electronics and operating systems.

The retention duration tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="30652" sha1="6qdff4ff37tj57akv2x09bq2wl88tjd" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups are primarily to [[data recovery|recover data]] after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive files such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. Unreadable sectors are then listed as numbers. 

Another way to verify data integrity is by testing the sequential reading speed. On Windows, the freeware "HDD scan" is able to generate a graph of the reading speed. Downspikes are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>6qdff4ff37tj57akv2x09bq2wl88tjd</sha1>
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      <contributor>
        <username>Elominius</username>
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      <comment>Not the same as "[[data recovery]]".</comment>
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      <text bytes="30661" sha1="ot6jn9r1d5kvs0dfxtnpse7usr3j26t" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive files such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. Unreadable sectors are then listed as numbers. 

Another way to verify data integrity is by testing the sequential reading speed. On Windows, the freeware "HDD scan" is able to generate a graph of the reading speed. Downspikes are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="31007" sha1="r9o00f01yf3q0ze3ykadcycenu7apl3" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="32961" sha1="m9v6ilzbd3ym6b4mng82b670tc9xobs" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

Optical media is ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2021.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt;

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="33999" sha1="cu4nczpgnss40llg704hiftnxx4w8ym" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Various types of data storage have benefits and disadvantages. As such, hard drives, optical discs and linear tape have the most reliability for archival storage. The latter two are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer disc (least cost) and up to 128 GB (multi-layer).

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to operate it infrequently only once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="34363" sha1="jh87l6ycu43xo9q52vybx4undj7k4kq" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]].
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="34482" sha1="6lt8jyhxaky8h89pa03oqbqu69s8u9h" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

=== Online services ===
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Elominius</username>
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      <comment>/* Online services */Separate h2 section for online services and mentioned a benefit of cloud storage for fairness.</comment>
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      <text bytes="36420" sha1="pg2rj8wed0zp88zkbubjnnf6gjksaoc" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, the simple reality is that you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="36393" sha1="iqqgf439uvdmgyw9og6t38dinf91hjq" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="36572" sha1="1cpjt1oqgtg9jxmk5y6zlaf8zs9ylh8" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <contributor>
        <username>Elominius</username>
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      <text bytes="37228" sha1="l49xg4xzxuctfqtd0qk8qy4ph7iacy1" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="37303" sha1="9ozvsewgq0gb6xek0jqbga77vz9th06" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="38384" sha1="s4l28cl7j9vgj8tx5h6b1tw2e1fsvuw" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>HendrixHammer</username>
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      <text bytes="38538" sha1="e0auu1zg15e1qqmdrphgcbvceyqv7x9" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="38567" sha1="naf1jd8h4ld7xrllyzfzs32npsjvo72" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]MobiKin Assistant for Android
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="38587" sha1="ciegqx3v35tkj7f8ixmy9xe6kf062u1" xml:space="preserve">In information technology, a backup, or [https://www.mobikin.com/assistant-for-android/ data backup], or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <text bytes="38538" sha1="e0auu1zg15e1qqmdrphgcbvceyqv7x9" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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        <username>Elominius</username>
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      <comment>/* Practices */ + classes of data</comment>
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      <text bytes="39752" sha1="3sbdwrxh9btvpvxif71cqz6eilkyy0d" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== Classes of data ===
You might want to classify your data by their level of importance.

'''First-class data''' is data that you never want to lose. '''Second-class data''' is data you prefer not to lose but losing them is not critical, or data that is relevant in the short term but you are unlikely to need in a decade. '''Third-class data''' are files that can easily be recreated or replaced or have no long-term value to you.

'''First-class data''' might be writings and scripts you worked a long time on, home videos such as family and honeymoon, important emails, and helpful web resources that have been or are likely to be taken down. '''Second-class data''' might be downloaded web pages or videos that are unlikely to be taken down, which you might have saved to read or watch them in places with no internet connection.  '''Third-class data''' are computer programs that can easily be downloaded again, temporary files, or [[:w:Cache (computing)|cached data]].

Data with a higher class should be backed up more frequently, and/or more redundantly. Consider creating an off-site backup of data you consider first-class. Third-class data requires no backups since losing that data is not critical.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
      <sha1>3sbdwrxh9btvpvxif71cqz6eilkyy0d</sha1>
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        <username>Elominius</username>
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      <text bytes="40363" sha1="kc4rraetcdoeu7rs2vsehfyso1iswwl" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Classes of data ==
Consider classifying your data by their degree of importance. Data with a higher class should be backed up more frequently, and/or more redundantly.

'''First-class data''' is data that you never want to lose. '''Second-class data''' is data you prefer not to lose but losing them is not critical, or data that is relevant in the short term but you are unlikely to need in a decade. '''Third-class data''' are files that can easily be recreated or replaced or have no long-term value to you.

'''First-class data''' might be writings and scripts you worked a long time on, photographs and home videos such as family-related and honeymoon, important emails, and helpful web resources that have been or are likely to be taken down. '''Second-class data''' might be photographss and videos that are not critical, and downloaded web pages or videos that are unlikely to be taken down, which you might have saved to read or watch them in places with no internet connection.  '''Third-class data''' are computer programs that can easily be downloaded again, temporary files, or [[:w:Cache (computing)|cached data]].

First-class data should be backed up at least twice, meaning after which the data exists three times.

If feasible, consider creating an off-site backup of any data you consider first-class. This can be a friend's house or a cloud storage service. This protects the data from natural disasters.

Second-class data should be backed up at least once, though a backup is not urgent if the data is stored on new media that is highly unlikely to fail anytime soon, or have fewer points of failure, such as optical discs. Second-class data on storage media expected to fail soon should be moved onto new storage media.

Third-class data requires no backups since losing that data is not critical.

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
{{reflist}}

[[Category:Backup| ]]
[[Category:Information technology]]</text>
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      <id>2675265</id>
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      <contributor>
        <username>Elominius</username>
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      <comment>/* Classes of data */ more examples</comment>
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      <text bytes="40680" sha1="rqjs35w6kivdqwazv3mdpj2vc2xwdni" xml:space="preserve">In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is "back up" (a phrasal verb), whereas the noun and adjective form is "backup".&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Backups primarily serve to restore the previous state after the loss, inadvertent deletion or corruption of data, and secondarily to recover data from an earlier time, based on a user-defined data retention policy.[3] Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan (DRP). One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup.&lt;ref&gt;[[Wikipedia: Backup]]&lt;/ref&gt;

Not only is a backup worth it to allow for restoration in case of data loss, but it will also allow you to rest assured knowing that your files are safe, similarly to having to worry less about injury when wearing a helmet while riding a bycicle. Data loss might cause an uncertainty of which memorable data is lost, if its date and/or the date range of the lost data is unknown.
[[:w:Murphy's Law|Murphy's Law]] states that "if something can go wrong, it probably will". As such, any data one does not wish to lose should be stored on more than one device.

== Causes of data loss ==
Data may be lost as a result of:

* Device failure
* Software bugs and poorly designed user interfaces
* Software lock-in
* Human error
* Overreliance on online services

For a more detailed explanation, read the sub page [[Backup/Causes of data loss]].

== Classes of data ==
Consider classifying your data by their degree of importance. Data with a higher class should be backed up more frequently, and/or more redundantly.

'''First-class data''' is data that you never want to lose. '''Second-class data''' is data you prefer not to lose but losing them is not critical, or data that is relevant in the short term but you are unlikely to need in a decade. '''Third-class data''' are files that can easily be recreated or replaced or have no long-term value to you.

'''First-class data''' might be writings and scripts you worked a long time on, photographs and home video recordings such as family-related and honeymoon, important emails, and helpful web resources that have been or are likely to be taken down. 

'''Second-class data''' might be a full backup of your operating system that is periodically overwritten with a new backup anyway, photographs and videos that are not critical, and downloaded web pages or videos that are unlikely to be taken down, which you might have saved to read or watch them in places with no internet connection.  

'''Third-class data''' are computer programs that can easily be downloaded again, temporary files such as [[:w:Archive_file|archive files]] (zip, 7z, tar) which were only created for sending files contained within, or [[:w:Cache (computing)|cached data]].

First-class data should be backed up at least twice, meaning after which the data exists three times.

If feasible, consider creating an off-site backup of any data you consider first-class. This can be a friend's house or a cloud storage service. This protects the data from natural disasters.

Second-class data should be backed up at least once, though a backup is not urgent if the data is stored on new media that is highly unlikely to fail anytime soon, or have fewer points of failure, such as optical discs. Second-class data on storage media expected to fail soon should be moved onto new storage media.

Third-class data requires no backups since losing that data is not critical. Third-class data may also be only stored on a cloud storage service without a local copy.

== Types of data storage ==
=== Magnetic and optical ===
Various types of data storage have benefits and disadvantages. As such, optical discs have the most reliability for archival storage, and hard disks are the most suitable for routine short-term backups.

Optical and tape storage are not vulnerable to data loss from mechanical failure, due to their modularity, as their controller is external rather than tied to the component that holds the data. In case of motor or loading mechanism failure of an optical drive, inserting a dull needle into the pinhole can force opening the tray to retrieve the media. Slot-load drives may require opening should the loading mechanism fail.

; Short-term
For routine short-term backups, especially disk image backups, external mechanical hard drives are the most suitable, since such backups involve much sequential writing, which wears down hard disks far less than flash storage. Hard drives just alter magnetic fields when writing data, and the head moves very little when writing sequentially, where as flash storage has to erase and reprogram memory cells, which wears it down. In addition, hard disks cost less than flash storage.

Linear tape storage could also be used for routine short-term backups, however, it is expensive and not user-friendly, has a high learning curve, and thus a high barrier of entry.

; Long-term
[[File:QPxTool DVD error rate graph.png|thumb|If supported by the optical drive model, software is able to measure the rate of minor errors on optical discs. The errors depicted in this graph are normal and well within a correctable range and have not corrupted any data.]]
[[File:Water running on CD-RW - label side.jpg|thumb|Optical discs are water-resistant and therefore have a good chance of surviving a flood disaster. ]]
Optical media does not have the vulnerabilities of other storage media such as head crashes and controller failures, making it ideal for the sporadic low-maintenance long-term archival of moderately sized chunks of data such as video recordings from an important event, at capacities available as of 2023, meaning 25 GB per single-layer Blu-ray disc (least cost) and up to 128 GB per disc (multi-layer). 

Higher-capacity optical formats such as the Sony Archival Disc exist, however, they are proprietary and vendor-exclusive, causing [[:w:vendor lock-in|vendor lock-in]].

Since optical discs are water-resistant and non-magnetic, they are the likeliest to survive a flood disaster or solar storm.

In addition, optical media can, if supported by the drive model, be scanned for impending integrity errors using software such as ''QpxTool'' and ''Nero DiscSpeed'', before any data loss occurs. A higher rate of still correctible errors suggests sooner data corruption, and/or media of lower quality.

Hard drive failure is mechanical and sudden, whereas optical media deterioration ("disc rot") happens slowly over time. Optical media is best stored in a cold and dry environment, whereas hard disk drives are less sensitive to heat and humidity while not in operation.&lt;ref&gt;https://smallbusiness.chron.com/temperature-should-laptop-hard-drive-run-81401.html&lt;/ref&gt;&lt;ref&gt;https://www.clir.org/pubs/reports/pub121/sec5/&lt;/ref&gt; However, humidity should be avoided ''during'' hard drives' operation, as it increases the likelihood of failure.&lt;ref&gt;https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/&lt;/ref&gt; ard drive motors' lubrication slowly loses effectiveness as well.&lt;ref&gt;http://www1.coe.neu.edu/~smuftu/docs/2011/ME5656_Term_Project%20Air%20lubrication%20in%20HDDs.PDF&lt;/ref&gt;  Hard drives' magnetic fields fade slowly over time, which could lead to logical data errors before the hard drive technically fails. For prevention, data would have to be rewritten once every few years. Proneness to such increases with drives' information density. The magnetic signal on magnetic tapes also fades over time, though manufacturers proclaim a "shelf life" of several decades for such.&lt;ref&gt;[https://searchdatabackup.techtarget.com/tip/How-to-estimate-the-lifespan-of-LTO-tapes How to estimate the lifespan of LTO tapes] – "30 years" ([http://www.fujifilmusa.com/shared/bin/LTO_Data_Tape_Seminar_2012.pdf source])&lt;/ref&gt; 

On hard disk drives, a slight possibility of manufacturing error leading to rapid failure exists.&lt;ref&gt;[https://www.kitguru.net/components/hard-drives/anton-shilov/hdd-expert-reliability-of-hdds-depends-on-manufacturing-process/ HDD Expert: Reliability of HDDs depends on manufacturing process – Anton Shilov, September 30, 2014, KitGuru]&lt;/ref&gt; If a hard drive is intended to be used for long-term storage, it is recommended to only operate it infrequently once written to, to minimize mechanical wear.

Humidity in an enclosed storage location can be reduced using silica gel baglets.

Optical media is the most likely to survive environmental disasters such as a flood, ionizing radiation from nuclear disaster, or the marginal possibility of an electromagnetic/solar radiation storm,&lt;ref&gt;[https://www.washingtonexaminer.com/washington-secrets/military-warns-emp-attack-could-wipe-out-america-democracy-world-order ''Military warns EMP attack could wipe out America'']&lt;/ref&gt;&lt;ref&gt;[https://www.youtube.com/watch?v=oHHSSJDJ4oo ''Could Solar Storms Destroy Civilization? Solar Flares &amp; Coronal Mass Ejections'' – Kurzgesagt - in a nutshell] (Video, 09m43s)&lt;/ref&gt;&lt;ref&gt;[https://www.gotquestions.org/EMP-attack.html ''Could an EMP attack be a part of the end times?'']&lt;/ref&gt; as it is water-resistant and has no internal electrical components vulnerable to [[:w:single effect events|single effect events]].

There exists optical media that is dedicated to archival, using silver, gold, or rock-like layers rather than organic dye, making it less sensitive to environmental conditions.&lt;ref&gt;[https://www.verbatim.com/prod/optical-media/dvd/archival-grade-gold-dvd-r/ultralife/ "Verbatim Gold" (silver and gold)] and [https://www.m-disc.com/technology.html "M-Disc" (rock-like)]&lt;/ref&gt;

=== Flash storage ===
Flash memory (solid state drives, USB sticks, memorybcards), while physically the most durable and usually fast, tend to be expensive per capacity, and might not be able to retain full data integrity for a long time (i.e. years), as the transistors which hold data in the form of electrical charge lose that charge over time.&lt;ref name=ni12&gt;{{cite web |date=2022-06-01 |title=Understanding Life Expectancy of Flash Storage |url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html |access-date=2022-10-18 |website=www.ni.com |language=en}}&lt;/ref&gt; This is also referred to as "bit fading".

Flash memory can be used for supplementary backups and short-term storage. However, the price per capacity is higher on flash storage than magnetic and optical storage. The main use of flash storage is for portable electronics and operating systems due to their physical sturdiness and immediate random access.

The retention duration on flash storage tends to be shorter with increasing data density, and deteriorates throughout weardown caused by repeated program/erase cycles. Life expectancy (program/erase cycles) also deteriorates with data density.  However, flash memory does not rely on moving mechanical parts that can fail like hard disk drives, hence the name "solid state drive". While USB sticks and memory cards are by definition also "solid state drives", the term is established to refer to larger-sized units for clarity. The lack of mechanical parts means that the flash memory does not wear down while idle unlike the spinning hard drive motor.

While powered on and idle, the flash storage's control firmware usually refreshes the information stored inside the sectors routinely.&lt;ref&gt;{{Cite web|date=2020-07-23|title=Understanding Life Expectancy of Flash Storage|url=https://www.ni.com/en-us/support/documentation/supplemental/12/understanding-life-expectancy-of-flash-storage.html|access-date=2020-12-19|website=www.ni.com|language=en}}&lt;/ref&gt;

Loss of data integrity is indicated by downspiking transfer rates caused by the flash memory controller attempting to correct errors.

Imminent failure of flash storage can be caused by power surges and voltage spikes. In comparison, hard disk drive controllers can also fail by such, but data stored on the metal disks, meaning a costly recovery may be possible, and optical discs can simply be retrieved as described earlier.

As flash storage is typically not intended for archival, and a possibility of component failure exists, anything stored on such that one does not wish to lose should be mirrored to at least one other location. For example, a large hard disk drive can be purposed to store corresponding disk images of flash media that are refreshed once in a while. This is especially recommended when storing a collection of frequently needed files or even an operating system on a flash drive, where scraping the files together or installing an operating system took time and effort, as a disk image allows sequentially reinstating the data onto the same or a different flash drive in case of error.

==== Memory cards ====
Mobile phone and tablet PC users may back up files short-term onto the removable memory card as an insurance against technical defect which denies access to its non-removable internal storage. 

This can be useful for photography and filming during a trip where cloud storage would be impractical due to possibly limited transfer rates and data plans unable to handle high-resolution imagery, and the protrusion of a flash drive connected through ''USB On-The-Go'' would compromise necessary ergonomy.

== Online services ==
{{anchor|Cloud_storage}}
Online services like cloud storage are just an '''extension''' and not a '''substitute''' to local data storage. Since cloud storage is a remote service rather than a personally owned product, the end user lacks technical control. Services might have varying retention spans and inactivity policies,&lt;ref&gt;For example, [https://help.dropbox.com/accounts-billing/settings-sign-in/email-about-inactive-account Dropbox retains unused accounts for up to one year].&lt;/ref&gt; and technical difficulties are not predictable to end users. Access requires internet connection, and transfer rates are limited by such. The slight possibility of erroneous account termination by a service provider exists as well.&lt;ref&gt;"Many people, incl. friends of mine, rely on ‘ cloud’ for file storage, use ‘ free’ messengers, listen to music on ‘ services’, and expect companies to provide stable and consistent service. This is what you get in the end: [GitHub account temporarily inaccessible]. I have always treated public services as a handout that could be taken away any moment, without any explanation, and their availability as a long-drawn moment between downtimes, data corruption or content deletion due to DMCA or other rules or laws, and favor self-hosted […]" — Twitter user ''@ValdikSS'', [https://twitter.com/ValdikSS/status/1116066219281592320 April 10, 2019 (multi-tweet)]&lt;/ref&gt;&lt;ref&gt;[https://karl-voit.at/cloud You Can't Control Your Data in the Cloud – Karl Voit]&lt;/ref&gt; However, Cloud storage can act as a supplementary and short-term off-site backup, such as during vacation.

The same principles apply to other online services such as email and social media platforms. Make sure services you utilize are equipped with [[:w:Data portability|proper export functionality]].&lt;ref&gt;[https://agb-server.web.de/webdeagb?target=_blank Web.de mail terms of service with six-month retention policy]: "We reserve the right to purge user data of accounts not logged into for six months, without notice. Additionally, after a year of inactivity, we reserve the right to release your email address for new registration." Original text: "WEB.DE ist berechtigt, die im Account des Nutzers gespeicherten Nachrichten und sonstige Dateien nach einem Zeitraum von sechs Monaten der Inaktivität (kein Login über Webbrowser, Mail-App oder E-Mail-Programm) ohne Rückfrage zu löschen. Nach einem Zeitraum von einem Jahr der Inaktivität ist WEB.DE darüber hinaus berechtigt, die vom Nutzer bei WEB.DE registrierten E-Mail-Adressen freizugeben und anderen Nutzern zur Verfügung zu stellen."&lt;/ref&gt;&lt;ref name=3things&gt;[https://www.youtube.com/watch?v=vDJHHjnWAoc&amp;t=01m02s ''3 Things I Wish I Knew when I First Started on YouTube'' (at 01m02s)] by Video Creators TV&lt;/ref&gt;&lt;ref&gt;[https://www.factmag.com/2015/10/21/janet-jackson-will-have-your-instagram-permanently-deleted-if-you-post-pictures-of-her/ ''Janet Jackson will have your Instagram permanently deleted if you post tour videos'' (FactMag, October 21, 2015)]&lt;/ref&gt;

Cloud storage may be less vulnerable to human error due to typically being managed by trained professionals, and takes the burden of maintenance away from the user. This is especially helpful to people with little [[file management]] knowledge.&lt;ref&gt;{{cite web |url=https://daringfireball.net/2014/09/security_tradeoffs |title=Security Trade-Offs |author=John Gruber |date=2014-09-03 |access-date=2023-01-21 }}&lt;/ref&gt;

For people who wish to create an off-site backup but have no separate location other than their residence, cloud storage is an option. However, as described in the section below, there are privacy risks.

=== Privacy on cloud storage services ===
If you use a cloud storage service, you need to expect that the people operating the service reserve the ability to access anything you upload to their computers.
It does not necessarily mean they will, but that they technically are able to.

Cloud storage operators tend to be reluctant to store any data on their computers that they can not view themselves. Even if they claim to encrypt your data, they might reserve a master decryption key.

If you are lucky, no human employee at the cloud service provider stumbles upon your files. Popular services have millions of users with a sheer amount of data that can not be overviewed by human staff. However, it is not guaranteed never to occur. Some artificial intelligence might mark your files as "suspicious", for example due to suspected copyright violations, putting them in a queue for human review.&lt;ref&gt;Text files containing simple numbers such as "1" have been detected as copyright violations by Google Drive: {{cite web |title=Googles Algorithmen stufen Ziffern als Copyright-Verletzung ein |url=https://www.heise.de/news/Googles-Algorithmen-stufen-Ziffern-als-Copyright-Verletzung-ein-6338468.html |date=2022-01-26 |access-date=2023-01-21 |language=de |author=Daniel AJ Sokolov }}&lt;/ref&gt;

== Environment ==
All data storage devices have a longer shelf life if stored in a cold and dry place such as a basement. For optical discs, the recommended temperature is at 15°C and 20°C (59°F and 68°F). Additionally, write-once optical media uses a light-sensitive dye, therefore is best stored in a dark location.&lt;ref&gt;[https://www.minimallstorage.com/blog/how-to-pack-and-store-dvds-and-disks-long-term/ ''How to Pack and Store DVDs and Discs Long-Term'' – Mini Mall Storage]&lt;/ref&gt;&lt;ref&gt;[https://www.clir.org/pubs/reports/pub121/sec5/ – 
5. Conditions That Affect CDs and DVDs – Council on Library and Information Resources]&lt;/ref&gt; 

If there is no spare space for optical discs such as a separate spindle, the cover sheet that is typically included at the top of a disc spindle, usually for labeling, can instead be used in the time being to separate empty and written-to discs.

Hard drives are less sensitive to heat, but more sensitive to humidity, and last longer if stored and operated in dry air.&lt;ref&gt;{{cite web |url=https://www.zdnet.com/article/heat-doesnt-kill-hard-drives-heres-what-does/ |title= Heat doesn't kill hard drives. Here's what does  |website=ZDNet |author=Robin Harris |date=2016-03-08 |access-date=2022-11-02 }}&lt;/ref&gt;&lt;ref&gt;{{cite web |url=https://www.backblaze.com/blog/hard-drive-temperature-does-it-matter/ |title=Hard Drive Temperature—Does It Matter? |website=BackBlaze |date=2014-05-12 |author=Brian Beach |access-date=2022-11-02 }}&lt;/ref&gt;

Flash storage is not subject to mechanical wear down, but can retain data for a longer time at lower temperatures. Should it lose data due to bit fading as described in [[#Flash_storage|§ Flash storage]], it is not physically damaged and can still be re-used for new data. As already mentioned, long-term archival is not the design purpose of flash storage. The primary uses for flash storage are in portable devices and for hosting operating systems.&lt;ref name=ni12 /&gt;

== Practices ==
=== Preparation ===
In a risky environment where there is an increased likelihood of data loss, such as a vaction or trip with the possibility of losing equipment, a higher backup frequency such as daily is recommended, which can be done at the base (hotel, holiday apartment, etc.) onto a portable hard disk drive or solid state drive.

For dedicated cameras and camcorders, memory cards can be cycled through.

=== File system structure image ===
For users who momentarily lack space storage for backups, an image of merely the file system structure, which contains information about file names, paths, fragments and time attributes, can significantly facilitate later data recovery in case of damage. Without this information, any damage affecting the file system header could lead to files being ''orphaned'' and only detectable by forensic software through file headers and footers. Fragmented files would need to be [[File_puzzling|puzzled together]].

The file system structure (or ''header'') is usually stored in the first 50 to 200 Megabytes, which can be captured using disk imaging software within seconds.

While such a backup does not contain file contents (except possibly those located at the earliest logical block addresses (''LBAs'') shortly after the file system header itself), it is a fallback solution which is better than nothing.

=== Verifying backups ===
Depending on the importance of data, backups should be verified once every few years. If at least three copies exist, one verification per decade should suffice. If one of the backups is no longer properly readable, a new one on fresh storage media can be created. 

The easiest way to verify backups and archives is to test whether a sample of randomly picked files is readable. 

For archive file formats such as ZIP and 7z and GZip, archive managers such as ''7-Zip'' on Windows and ''File Roller'' on Linux have a feature for verifying data integrity and listing corrupt files. For entire devices such as hard drives and optical discs, tools such as the &lt;code&gt;badblocks&lt;/code&gt; command on Linux and the freemium [[:w:shareware|shareware]] "IsoBuster" on Windows can be used to scan for unreadable sectors. On IsoBuster, sector scanning is part of the free features. These tools list unreadable sectors as numbers.

Another way to verify data integrity is by measuring the sequential reading speed. On Windows, the freeware tool "HDD scan" is able to generate a line graph of the reading speed. Ideally, the line is smooth. On flash storage, it ideally is straight and flat with minimal downspikes at most, and on spinning media such as hard drives and optical discs, the speed slightly decreases or increases due to the changing circumference per rotation where speeds are higher at the outer edge.  Significant downspikes in speed are a hint to damage since the data storage controller has to spend effort correcting errors. For optical media, error rate scanning is available as described in [[#Magnetic_and_optical|§ Magnetic and optical]].

Unused flash storage would have to be verified at least yearly to prevent losing data, since the process of reading causes the flash memory controller to refresh the data.&lt;ref name=ni12 /&gt; However, as stated earlier ([[#Flash_storage|§ Flash storage]]), flash memory is not ideal for archival to begin with due to bit fading and higher price per capacity.

=== Cloning ===
Cloning is the practice of copying each bit from one data storage device sequentially to another. On Windows, this task can be performed with third-party software and on Linux with the &lt;code&gt;dd&lt;/code&gt; command-line tool. Special caution should be taken not to select the wrong target device.

If your computer has a modular, replaceable data storage device, it can be replaced with a cloned data storage device in case of failure, allowing for resuming work with only minimal time loss.&lt;ref&gt;{{Cite web|url=https://discussions.apple.com/docs/DOC-6031|title=Methodology to protect your data. Backups vs. Archives. Long-term data protection - Apple Community|date=2014-06-14|website=discussions.apple.com |access-date=2023-02-08 |quote=In case of an internal HD crash and failure, there is absolutely nothing quicker to getting back to 100% operation than having a HD clone handy to either boot from, or within 20 mins. installing and removing the bad HD. Nothing to install software-wise, and a speedy immediate return to your computer use and productivity. }}&lt;/ref&gt;

=== Other tips ===
* {{Visible anchor|lostBackup|text='''Lost backups:'''}} If you are unable to physically locate a data storage device which contains a backup, act as if it were lost and consider just creating another backup from the source. The time and effort spared by foregoing to search for the lost device might be worth it. In case it is found again, one has one more redundant backup. If the redundant backup is not necessary, one of the storage devices can be re-purposed.
** The same applies to individual files you are not sure where you have already backed them up to. Back them up again, and to prevent losing track of files, create [[File management/Directory structures|logical structures of directories]]. In effect, the accessible copy of a file "seeds" that file to a new backup so you have at least two accessible copies.
** If you are certain that the data is backed up on a different device, you can store a redundant copy in a folder named "duplicates" or "possible duplicates" for the time being.
* {{Visible anchor|distinctBackup|text='''Distinct backup media:'''}} Backup media distinct from its source media prevents failure at a similar time from a common cause such as a manufacturing error.
* {{Visible anchor|lastbackup|text='''Tracking manual backups:'''}} Manual backups of individual directories can be tracked using a text file such as &lt;code&gt;lastbackup.txt&lt;/code&gt; or &lt;code&gt;backupinfo.txt&lt;/code&gt;, containing the time of the last backup and optionally additional information such as the name of the backup device.
* {{Visible anchor|reputableBrands|text='''Reputable brands:'''}} Data storage not from reputable and trustworthy brands or pre-owned should not be relied upon in long term, only for temporary storage, testing purposes, and similar.
* {{Visible anchor|proprietaryFormats|text='''Proprietary formats:'''}} Software that stores backups in proprietary formats such as that of Acronis (&lt;code&gt;.tib&lt;/code&gt;) should be used with caution due to the possibility of [[:w:vendor lock-in|vendor lock-in]]. Should said vendor cease operations, it could become even more difficult to access archives in proprietary formats in the long term.
* {{Visible anchor|encryption|text='''Encryption:'''}} In the long term, encrypted backups and archives pose a risk of forgetting or losing the access credential (e.g. password). When using encryption, weigh the likelihood of physically losing the data storage against aforementioned risk, and factor in the sensitivity of data. For example, public web downloads usually don't need to be encrypted.

== Compressed archives ==
=== Compression ratio ===
Compressed archives may be used where efficient, such as for text documents and code, where strong compression formats such as 7-Zip (LZMA) and XZip could reduce size by a factor of 100 or more. Uncompressed bitmap images can achieve compression ratios of around 10; more or less depending on content.

Binary data such as multimedia (picture, video, audio) that has already been internally compressed can not be effectively shrunk by applying additional compression to it, as most redundancy has already been defeated by internal compression.

Which level of compression one should use depends on the contents. For example, for creating an archive file containing pre-compressed data such as PNG files, compression can be deactivated entirely for the highest performance, since data does not have to be encoded and later decoded during extraction. For text-based data, a high compression level is highly effective. For archiving disk image files and mixed data with varying levels of compressibility, weak compression is recommended for a minimal impact on performance while still significantly compressing blank parts ("[[:w:Solid_compression#Explanation|air]]") of the image and text-based files. Performance matters on disk image files due to their typically large size.

=== Magnification of damage ===
[[File:Aicp homescreen.bitflip glitch art.rerender.png|thumb|Damage on a PNG image from flipping a single bit]]
It should however be considered that the slightest damage to a compressed archive file could magnify enormously, possibly rendering the rest of an inside file or the entire archive useless. The scope of the damage depends on compression method, where [[:w:Solid compression|solid compression]] causes the latter, as it deduplicates information across contained files to maximize compression effectiveness. As such, it is recommended to store compressed archives on no less than two devices. 

If a separate device is unavailable, storing a duplicate of the archive file on the same device for redundancy could still allow repairing errors in uncommon locations by merging the intact parts using a byte editor (or "hex editor"), though errors are difficult to locate if the storage device controller's firmware returns damaged data to the computer without reporting it as such. Some flash storage devices may return sectors (512 bytes each) with damaged data as null bytes. In that case, a multiple of 512 sequential null bytes between binary data suggests a logical error in the file. On optical discs, a sector typically has 2048 bytes.

To get a visualized idea of how fragile compressed archives can be to damage, try opening a PNG or TIFF image inside a byte editor (or ''hex editor''), and edit only few bytes somewhere near the middle, and then try the same on an uncompressed bitmap (BMP) for comparison. The PNG and TIFF images are to be completely demolished and glitched out from the damaged point, while effects on the uncompressed bitmap are only pinhole-sized. 

This experiment might not be as effective on a JPEG image as on PNG and TIFF, as its compression algorithm is more robust against damage. It may cause some gitching and hue alterations on ordinary JPEG, and ''digital stains'' on progressive JPEG, but nothing that demolishes the entire image beyond repair. For reference, see the [[:Commons: category: Bit-blending]] experiment.

Compression formats that have a weaker ratio, but in return require far less computing efforts, might use block-based storage, where information is stored in compressed blocks of a fixed size. Data blocks after a damaged one might be recoverable. A popular block-based compression format is Gzip; see [[:w:Gzip#Damage_recovery|Gzip § Damage recovery]].

=== Efficiency ===
Human-readable text and code is highly compressible, and archive formats' internal file systems typically handle a high number of small files more efficiently than data storage file systems. 

On FAT32/16/12 and exFAT for example, any non-empty file reserves at least one entire cluster (space allocation unit), which may be preformatted to around 16 to 256 KB, depending on total storage size. Too many small files cause space being wasted through ''cluster overhead'', whereas archive formats handle many small files efficiently, even with compression deactivated.

However, digital photographs and video are internally compressed to a degree where additional compression through an archive format such as ''Zip'', ''RAR'', and ''7z'' would not shrink the size effectively while significantly slowing down extraction speeds rather than allowing for direct playback, and making it vulnerable to damage.

Note that a ''[[:w:program stream|program stream]]'' video (most mobile video) with an end-of-file ''[[:w:moov atom|moov atom]]'' depends on completeness or else be unplayable. This is not the case for ''[[:w:transport stream|transport stream]]'' video, frequently used by dedicated camcorders such as those of Panasonic and Sony ([[:w:AVCHD|AVCHD]]).

== Preventing data lock-in ==
Wherever you store your data, verify in advance that proper export functionality exists.

For example, as of 2022, the email service "ProtonMail" lacks support for email protocols like POP3 or IMAP. The only way to back up messages is individually downloading them, which is impractical, since individually downloading one thousand emails could take several hours of repetitive clicking.

On the Android mobile operating system, applications might store user data inside the &lt;code&gt;/data/&lt;/code&gt; folder. This includes web browsing session, history, and saved pages depending on the browser. This makes it only accessible to the application itself. In other for any other application to access it, [[:w:Rooting (Android)|root access]] must be unlocked.&lt;ref&gt;[https://beepb00p.xyz/exports.html Building data liberation infrastructure – Beepb00p.xyz]&lt;/ref&gt;

== Format obsolescence ==
There is a slight likelihood that formats used today will become unsupported in future.

A past example is the HD-DVD, an optical disc format which [[:w:High_definition_optical_disc_format_war|did not succeed in the market]]. Unlike DVD plus and minus formats, HD-DVD could not successfully co-exist with its competing format, the Blu-ray disc, and production of HD-DVD media and hardware was halted. As a result, people might have recorded data on HD-DVD discs, but no longer own a drive that reads them. A Blu-ray drive could technically read HD-DVDs, since they are technically very similar and use the same wave length, but optical drive manufacturers see no need in implementing HD-DVD support.

== Other areas ==
=== Web browsing ===
==== Sessions ====
Develop the habit of exporting your browsing session into a text file regularly, which can be done through a browser extension. The automatic session restoration might fail, and the session database might have a proprietary format only readable or decodeable through difficult-to-use tools rather than a simple text editor.

Some browser extensions allow exporting both page title and URL, facilitating later searching. Some extensions have an option to limit the export to only tabs of the current window, which could be of use if tabs in other windows have not been changed.

Some browser extensions have an internal session manager, while others export the session into a file in the download folder. Some might have both. Some extensions for this purpose have been discarded as a result of Mozilla Firefox, one of the most popular web browsers, deprecating support for extensions in a legacy format with the transition to version 57 "Quantum", though functionally similar surrogates are presumed to be released.

==== Web forms ====
Web form data may get lost as a result of browser crashes caused by RAM exhaustion, operating system crashes or power outages without uninterrupted power supply (external unit or laptop battery), or a failed form submission.&lt;ref&gt;Data from failed form submissions may be recoverable through a "core dump" generated from the browser's process, for which you may refer to [https://superuser.com/questions/236390/how-do-i-recover-a-form-in-firefox-without-installing-a-plugin/236400#236400 this guide by Joey Adams].&lt;/ref&gt;

Browser extensions such as ''Textarea Cache'' prevent loss of form data by backing it up automatically.&lt;ref&gt;[https://addons.mozilla.org/en-US/firefox/addon/textarea-cache/ Textarea Cache for Firefox]&lt;/ref&gt;

Sites for which this is not wanted can be added to an exclusion list in the extension's settings.

Consider drafting any text that is presumed to take minutes or longer to write into an offline text file, from which it can be copied and pasted into a web form.

The same also applies to other areas such as to programs' internal text areas like the WinRAR archive comment field&lt;ref&gt;https://documentation.help/WinRAR/HELPArcComment.htm&lt;/ref&gt;, since it may be discarded in case of an error or cancellation. Regarding WinRAR, using proprietary formats is not recommended anyway due to potential incompatibility throughout systems.

==== Browsing history ====
Web browsers might automatically delete history under certain conditions such as space storage exhaustion on the partition that stores the user data folder (or "profile folder"), or history from earlier than a time threshold such as three months. An update might unexpectedly change the retention duration, discarding history falling outside if shortened.&lt;ref name="obsidian"&gt;{{cite web|last1=Benson|first1=Ryan|title=Archived History files removed from Chrome v37|url=http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|archive-url=https://web.archive.org/web/20141010125418/http://www.obsidianforensics.com/blog/archived-history-files-removed-from-chrome-v37/|url-status=dead|archive-date=2014-10-10|publisher=Obsidian Forensics|ref=obsidian}}&lt;/ref&gt;

If you wish to retain history beyond browsers' retention span, consider routinely creating copies of the history database. Firefox's live database file is named &lt;code&gt;places.sqlite&lt;/code&gt; and located in the profile folder. For Google Chrome/Chromium, extensions exist that allow exporting it into the download folder.&lt;ref&gt;[https://chrome.google.com/webstore/detail/export-historybookmarks-t/dcoegfodcnjofhjfbhegcgjgapeichlf Export History/Bookmarks to JSON/CSV*/XLS*] extension from the Google Chrome web store&lt;/ref&gt;

Note that on mobile phones, [[File_management#On-device_management|restrictions by operating system]] could deny file-level access to browsers' user data. Then, the only way to export browsing data is using a mobile browser which supports third-party extensions, such as the Chromium fork "Kiwi browser", which is compatible with many desktop Google Chrome extensions.&lt;ref&gt;[https://kiwibrowser.com/features/ Features - Kiwi Browser]&lt;/ref&gt;

=== Paper ===
Reliable long-term storage of relatively low amounts of data onto paper is possible using software such as ''[http://ollydbg.de/Paperbak/ PaperBak]'' ([https://github.com/Rupan/paperbak open-source]), which can encode digital data into printable machine-readable matrix bar code.

Paper books can not be duplicated as simply as digital computer files, but have supreme longevity and reliability due to immunity from technical failure. Abstractly, paper is a form of optical media.

Backing up paper books themselves may be desirable to protect against short-term losses such as forgetting to take them after use at a location such as school, university, or work place. Pages can be individually digitized in a high quality using optical flatbed scanners, though the process is slow and demands patience. It is faster and more conveniently done using a digital camera, preferably monuted to a tripod pointing down for a fixed position of the pages within the images, and in good lighting. Pairs of pages can be photographed individually, though filming while quickly skimming through the pages is the fastest method. The necessary resolution for clear readability depends on size and clarity of font, but at least 1080p is recommended, where each still frame of the video acts as a 2.1-Megapixel photograph, only with slight quality losses from video compression.

== Commercial Backup products ==
Different commercial products provide Backup and recovery capabilities such as [[Commvault]], [[Veritas NetBackup]] and [[Veritas Backup Exec]], [[Veeam Backup &amp; Replication]], [[Arcserve]].

== Activities ==
# Read about [[w:NDMP]] (''Network Data Management Protocol'')
# Learn about [[RPO]] and [[RTO]]

== See Also ==
* [[Data recovery]]
* [[Database Fundamentals/Backup and Restore]]
* [[Oracle Database Administration/Backup and Recovery]]
* [[Linux server administration/Backup and Restore]]
* [[Disk arrays|Disk Arrays]]
* [[Wikipedia: Backup]]

== References ==
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