This article provides some guidelines for the preservation of digital data using CDs and DVDs. This information has been gathered from a number of sources including NIST (National Institute of Standards and Technology), DVD and CD manufacturers and data archiving specialists.
The consensus of opinions, based on accelerated lifetime testing, is that a high quality CD or DVD, if properly handled and stored, should preserved data for at least 75 years. Some studies even suggest a lifetime as long as 200 years before the data becomes unreadable.
Of course whether the hardware required to read a current CD or DVD will be around in 75 or 200 years is another matter. Most system today don't have even the hardware to read 5.25" floppy disks (which were common and popular only 10 years ago).
The key points here are that long life depends on using HIGH QUALITY archival DVDs and CDs and handling and storing them properly. The less you handle them, the better, so for real archival use, make two copies. Put one away in storage under the conditions outlined below (vertical storage in a case under low temperature and low humidity conditions) and use one as your "working" copy.
A standard jewel case is adequate for storage. In jewel cases,the disc is suspended by the center hole and isolates the written area [read side] from contacting any surface, It also offers some protection against rapid temperature changes
"The worst handling stresses for a CD are caused by severe flexing or application of a sharp point to the top surface" - Kodak
"Cheap plastic sleeves (for example, those sometimes used to hold CDs in the backs of books or in some types of multiple CD holders) are not suitable for long-term storage" - Kodak
Writable CDs are made using several different photosensitive dyes:
|Metal-Cyanine||Blue||Original CD-R Dye, Least stable|
|Metal-Azo||Very Deep Blue||Increased stability over Cyanine dyes|
|Phthalocyanine||Very light Green||Most stable, transparent and durable|
|When stored under optimum conditions, CDs using Phthalocyanine dyes and a gold metallization layer should have the longest life. Mitsui MAM-A Gold Archive 74 minute CD-Rs match these requirements. They are a little more expensive then "regular" CD-Rs, but still only about $1.50 each in quantity.|
|Delkin's eFilm Archival Gold CD-R's incorporate a Phthalocyanine (thalo-sy-a-neen) dye and a 24k gold reflective layer into every CD-R. Delkin claim that eFilm Archival Gold CD-R's can store images for more than 300 years. I'm not aware of any independant tests that verify this, but gold/pthalocyanine disks should have the longest lives.|
It's a little more difficult to make specific DVD recommendations as DVDs haven't been quite so well
characterized as CDs. Certainly some are more archival then others, though it's hard to specify a particular
product right now. It's almost certainly true the cheapest, spindle bundled, multipack DVDs aren't going to have
the longest life though. Verbatim claims a projected life of 100+ years for their Metal-Azo DataLifePlus series of DVDs, if stored in jewel box cases
in a non corrosive atmosphere at 25C and 55% RH. However I don't know of any independent
study of DVD lifetimes.
One thing you may want to do if your data is really important is to make multiple backups and don't store them togther. While any one disk can fail or be accidentally damaged, the chances of that happening to two disks at the same time are much lower.
CD Check - A freeware program (for personal use) which can check the integrity of data on a CD.
Stability Comparison of Recordable Optical Discs : a Study of Error Rates in Harsh Conditions