Optical media, such as CD, DVD and Blu-ray disc can play a valuable part of a secure image storage strategy.
CD, DVD, and Blu-ray discs provide a cost-effective and forward-compatible way to backup or transfer your images and footage. Because so much content (music and movies) is distributed in this format, it’s likely that players for these discs will be available long into the future — hopefully long past the time when you have migrated your backup storage to some other medium.
While the capability of playing optical discs will be available long into the future, the particular discs you burn today may not be so lucky. Data stored on an optical disc can degrade at an unknown rate, leaving you with discs that are partially or totally unreadable. There is a lot of conjecture and bad information floating around about the longevity of optical discs, but the truth is that we don’t know how long any particular one will last.
With proper handling, a quality optical disc that is burned well should be a valuable backup to a hard-drive-based archive for 5 to 10 years. We’ve done data validation experiments on the DVDs, and have found little evidence of data degradation on properly stored discs. However, you should be careful to avoid writing on the tops of discs or using adhesive labels. A safer choice is to write on the clear plastic inner ring or to use discs that feature a surface specifically designed to hold an inkjet print.
FIGURE 1 There are three disc types with the same form factor - CD, DVD, and Blu-ray. They can provide an important disaster recovery backup function.
The CD, or Compact Disc, is a popular format but, because of their small storage capacity (682 MB), CDs only make sense for photographers who shoot JPEGs rather than raw files. Manufacturing defects and poor storage conditions can result in data loss. Gold foil CDs are considered to be the best quality. Rewritable discs are inherently less stable than write-once discs.
DVD can be a very good option for backups at the present time, depending on how much data you create. DVDs are relatively stable, hold large amounts of data (4.7 GB or 9.4 GB), and should be readable for quite some time to come. Manufacturing defects and poor storage conditions can result in data loss. Two brands of DVD that are considered particularly stable are Delkin Gold and Taiyo Yuden.
DVD+ or DVD-?
The DVD+R format is more modern than DVD-R and includes some newer error-correction technology, and is therefore a better choice for archive discs. However if you are creating a DVD to playback a video file, the DVD-R format tends to offer broader compatibility.
In early 2008, the format war between Blu-ray and HD-DVD ended, with Blu-ray victorious. Blu-ray discs are the same physical size as CDs and DVDs, but hold either 25 or 50 gigabytes. Blu-ray players and recorders should always be able to play or record CD and DVD media. Recent changes in disc manufacturing technology have resulted in Blu-ray discs selling for roughly the same price as DVD blanks.
While there is not a long track record for Blu-ray discs, the underlying technology should provide stable long-term backup. Because the format is so new, there is no consensus on which brand of discs to use.
In order to maximize the lifespan of optical discs, we suggest the following precautions. Note that this is for discs that need to last as long as possible. For discs that are used for delivery only, or any other temporary use, feel free to break any of these rules.
- Use quality discs. This is outlined above, in the section for each disc type.
- Don’t use a solvent-based pen to mark the disc. The solvents can migrate through the plastic and damage the recording surface. Use only “CD safe” markers (available at computer or office supply stores) and mark only in the center area of the disc.
- Do not put label stickers on your discs
- Don’t print with inkjet printers – inkjet inks also contain solvents. If using inkjet printing, be sure to use specialty discs that contain a printable surface and hard matte finish.
- Store your discs immediately in a way that protects them from scratches.
- Don't pull discs from jewel cases by the edges. Instead, push down on the center button or tines to release.
- Treat your disks gingerly. Although they are cheap to make, they can have very high value if catastrophe hits your hard drive archive.
There are several ways you can store your discs. They are listed here from the least secure, but lowest cost, up to the most secure and expensive.
When you buy discs in bulk, they are often packaged in cakeboxes. These are very efficient from a space perspective, but offer little protection to the discs themselves. Not only are the discs subject to scratching, due to foreign matter that might get between the discs, but any time you actually need to find a disc, you'll run the risk of scratching the discs you are looking through. Cakeboxes should not be used for any discs that you will count on for long-term access.
CD notebooks, like the one pictured in Figure 2 are cost-efficient ways to store discs, with good protection from handling scratches (depending on the construction of the storage page). These are available at low cost from music and electronics stores. You can purchase archival pages for optical disc storage pages from outlets like Light Impressions. Note that notebooks may be inappropriate for use in high-humidity environments where discs might stick to the plastic of the pages.
There's a reason discs come in Jewel cases. This is the safest way to store a disc. The disc surface (both top and bottom) is suspended so that nothing touches it. Of course, Jewel cases make a backup archive take up significantly more room than notebooks do. Instead of a spot on a shelf, you need a piece of furniture. If you have both the space available, and the paranoia, Jewel cases are the most secure.
FIGURE 2 These are the various methods for storage of optical discs. Notebooks are the best balance of price and security.
Write-once discs are the only kinds of discs to use for backup and may be validated with a very high level of certainty. With write-once discs, it's possible to know that all the data written to the disc is still available, down to the last bit. We have a complete write-up, including movies, in the Data Validation section.