Backup has become a word that has become synonymous with online solutions. However, also having a physical copy of your data in the form of optical media is a wise decision for many reasons. It de-centralizes the data and means that access to it is not dependent on your computer. It removes dependence on third-party backup services, and it also establishes a means by which data can be independently transferred to a third party if so desired.
The challenges that go along with choosing optical media to store data however mainly come to down to two big issues. The first of these is that as data storage needs have mushroomed in size, the media needs to have sufficient storage capacity to be practical. And secondly that it needs to be sufficiently robust to safely store data over the time period when it will be accessed. The choices of optical media for digital archiving currently come down to three main options (although several more are in current development).
1/ CD-R – These typically offer storage of around 700mb. The specification for CD-R was first published in 1988, but it wasn’t until 1995 that the first recorder that cost less than a $1000 was introduced (the Philips 4020i). But now CD-R recorders are ubiquitous on virtually all computers. The quality of CD-R discs does vary tremendously. But even average CD-R discs have been shown to typically last for 10 years, according to research by J Perdereau, so many people’s fears about degradation are largely unfounded.
Bear in mind though that most storage problems with optical media are attributable to issues with the initial burn of the disc. So it’s essential that as soon as you have burned any media to any type of optical storage that you check it has copied over the data correctly.
The two main types of degradation that occur after the initial burn are because of the dyes and the reflective surface. Both of these have improved over the years, but you should still double check manufacturer claims as to life expectancy. For longer term data storage it is a good idea to look at gold-based reflective surfaces on your CD-Rs (as opposed to silver) because they do not suffer from oxidation.
2/ DVD-R – These typically store 4.7GBs of data, although it is possible to get double-sided, double-layer discs that will store up to 17.08GB. The quality of the discs is a big factor in how long they will last, but in tests this has been shown to be anywhere between 2 and 15 years, with the National Institute of Standards and Technology (NIST) finding in its tests that there is greater variability with DVD-R in archival longevity then for CD-R. So, if your archival needs are modest then CD-R is probably a better choice.
3/ Blu-Ray – A normal single layer Blu-Ray Disc holds 25GB of data, while a double-sided one holds 50GB. Commercially Blu-Ray has not caught on as much as was earlier predicted, largely due to the quick growth of broadband speeds and the rise of online streaming in the United States. But as an archival format it offers the greatest capacity of any of the current mainstream optical media solutions. In one French Study into its longevity it was concluded that Blu-Ray (HTL) discs produced by Panasonic and Sony offered the greatest reliability for archiving, and that Blu-Ray (LTH) discs should be avoided for this purpose.
Each of the different storage solutions offers a cheap and easy way of backing up your data. They allow you to have your data in a properly portable format and release you from total dependence on external services. However, while you should have a backup copy of your data in a physical archival format, such as the three I have described, it should not be your only backup due to uncertainties about long-term data storage. So you would also be wise to additionally have an online digital backup in place as well.