Storage Media

The term storage media refers to any number of objects - CD, DVD, USB flash drive - basically any device that can have any form of data stored on it.

When deciding where to keep your data, remember that everything rots, and everything breaks down. It's the way the universe works, and there's not much we can do to stop it. Therefore, you have to think about your data's lifetime in terms of months, years, or decades.

Very little data most people have truly needs decades of preservation, but often, it doesn't hurt to have it around as long as possible. A minor amount of effort will help mitigate that. Specifically, expect to renew/refresh your data storage every 3 years or so - anything you don't do this with will progressively be subject to bit rot, moisture and heat damage, and being shoved into progressively unpleasant locations at home and office before someone decides it's trash.

More information about bit rot can be found on the Wikipedia article.

Optical media

The major strength of optical media is that the storage media is a separate unit from the drive, meaning the media can be placed in a new drive in the event of a drive failure. This is not possible on hard drives (at least not easily^[1]) or flash drives. If the storage controller of a hard drive or flash storage fails, the data is locked in.^[2] In addition, write-once media has the benefit of being inviolable by malware such as ramsomware.

Compact Disks, Digital Video Disks, High Definition DVDs (HD-DVD), and Blu-Ray (BD) are all optical media. This means that information stored on them is read by a laser. It is debated how long the shelf lives of these products are, while commonly accepted that DVDs have a shelf of 20 years, it is unknown obout the others (some of these technologies haven't existed long enough to know this). The Forensics Wiki contains some info on retrieving data from them; ISOdisk is a good tool for Windows. See also [1].

Compact Disks (CD)

CDs store only up to 700 MB and have only a single layer, which is little capacity by today's standards. The only use case is a car audio player that does not support flash media (USB sticks and SD cards).

Digital Video / Versatile Disks (DVD)

As with CDs, DVDs that are professionally produced have a longer shelf life than recordable ones, although there is less agreement as to how long they last. 4GB on a single layer, double that on a dual layer. Generally not recommended as much as hard drives by today's standards (unless you can't use your hard drives for whatever reason).

High-Definition Digital Video / Versatile Disks (HD-DVD)

HD-DVD (Toshiba, mainly) is dead and buried, having lost the format war to Blu-Ray (Sony). For this reason, it is best not to invest too much into novel formats that are not widely established. It is recommended that you back up any data from an HD-DVD and transfer it to another format. You probably wouldn't be able to find any empty HD-DVD disks to use for archiving, so don't try.

Optical disc formats that predate HD-DVD (meaning CD and DVD) are still supported by drive vendors for the reason that many people already own them. CDs and DVDs are still being produced due to their lower price and because many households already own devices that can read them (Network effect).

Blu-Ray (BD)

So named because of the blue laser needed to record and read a Blu-Ray disk, Blu-Ray is the newest optical media available. A normal Blu-Ray disk is able to store 25 GB on a single layer, or 50 GB for a dual layer. In 2010, the BDXL format was released, ranging up to 128 GB, but are not supported by existing Blu-ray drives.

Blu-ray storage is more expensive per gigabyte than hard drive storage and has less space per unit. However, as an optical format, it doesn't have the points of failure that other types of storage devices have, and is therefore expected to last a decade at the very least. Discs by high-quality vendors are of course expected to last much longer than that.

A derivative format of the Blu-ray disc is the "M-Disc", which is advertised to be able to preserve data for a thousand years. While they can be read by existing Blu-ray drives, special optical drives are required to be able to write data to them (usually labelled with "M-Disc"), and M-Discs cost several times as much as a conventional Blu-ray disc. The advantage of them over regular high-quality Blu-rays is unclear. M-Discs were originally developed to replace organic dyes in DVD layers with a more stable inorganic formula. However, Blu-rays use inorganic dyes by default, and discs with organic dyes (LTH) must be explicitly marked and seem to be rare as of 2024.

Sony Archival Disc

The Archival Disc is a discontinued proprietary format that makes use of stacked Blu-ray discs in a cartridge. While the benefit over traditional Blu-ray discs is a higher storage capacity per unit, the benefit is defeated by the fact that Sony discontinued production of Archival Disc drives, and other vendors do not support the format (Vendor lock-in).

Given that discs in a cartridge rely on complicated mechanics rather than a simple rotary engine found in traditional optical drives, an Archival Disc drive has more points of failure than a traditional optical drive.

Hard Disk Drives (HDD)

There are many forms of hard drives, including internal hard drives for laptops (2.5") and desktops (3.5"), and external hard drives that can run free of a computer. While external hard drives fall under the replace-every-few-years rule, data can be bought cheaply in comparison to other formats ($80 could probably buy two terabytes of storage), and so are the recommended format used for backups.

Since hard drives have points of spontaneous failure (head crash and storage controller), a single hard disk drive should not be relied upon for long-term archival of any data.

Hard drives that are intended for long-term archival should only be accessed rarely to minimize wear. Any hard drive should either be used for long-term cold storage or frequently accessed short-term storage.

External Hard Drives

These are regular internal drives fitted into an enclosure, usually with a USB cable for connectivity. Functionally, they are more or less like using a thumb drive. Externals are quite cheap these days, and can be bought for as low as $80 and $130 for a 2TB and 5TB respectively. For a bit more, you can buy drives with smaller form factors and USB power. They're a very affordable way to keep your data backed up.

Network Attached Storage (NAS)

Unlike external hard drives which are dependent on a host PC, a NAS is more or less its own computer. They contain slots for one or more HDD (or come with them built-in), an ethernet port and such basic features as print server, file server, BitTorrent client, etc. This allows them to function independently of any PC, allowing any computer on the network access. A good NAS will set you back $150 or more depending on available drive bays, bundled drives and feature set.

Hard Drive Docks

HDD Docks are essentially enclosures for multiple HDDs. Like an external hard drive, they usually connect to a single computer via USB. Lacking the fancy features of a NAS, they can be significantly cheaper, and have the advantage of requiring only one power socket and USB cable for multiple drives, as opposed to the requirements of a legion of individual externals.

Linear Tape Open (LTO)

Digital LTO tapes can store several terabytes of data per unit for decades, and individual tapes are cheap, but the tape drives are dozens of times more expensive than an optical drive, and tapes lack random access, so any non-sequential access of data would be very slow.

Since tapes do not behave like usual block devices (hard drives and flash drives), tape drive support by operating systems is uncertain and may rely on third-party software, making it less user-friendly.

References