Answers to your questions about CD/DVD archival capacity and testing
By Tom Peterson, Product Line Manager for Rimage Corporation
Professional photographers need clear answers to their questions about using CDs and DVDs as archival media. What causes data loss in CDs and DVDs? How do you avoid that? What is an archival CD/DVD? How do I find archival quality CDs/DVDs? How long should my data last on archival quality CDs/DVDs? What is Blu-ray technology? Do I need it?
Tom Peterson is the Product Line Manager for Rimage Corporation, providers of CD-R and DVD-R publishing, duplication and printing solutions. He is responsible for the purchase of more than two million CD-Rs and DVD-Rs each month for the company and meets monthly with representatives of all major media manufacturers to keep abreast of changes in technology. Peterson led the initiative within Rimage of working with vendors to establish the Rimage 100-year media warranty.
We asked Peterson to provide the answers you wanted.
What conditions can contribute to data loss in CDs and DVDs? (aside from breakage and splitting)
The first step in ensuring a long life for a CD or DVD is to obtain a good recording. Many people assume that since the recording is “digital,” it is either perfect, or bad, and that there are no degrees of quality.
When you record data on a CD, the drive places your data in non-adjacent locations. For example, this sentence might be spread over several different spots on a CD. Then the drive uses algorithms to error check and auto-correct if a piece of data is wrong. With these techniques, the drive can reconstruct your data, even if some pieces are missing.
A good quality recording results in very little error correction by the drive. A poor quality recording means that from day one, the drive has to do a lot of error correcting to play or read your disc. If the disc is marginal to begin with, and ages or degrades at all, you can have an unreadable disc in six months.
Here are a few tips for how to properly store and handle a CD or DVD for maximum life:
- Avoid temperature and humidity extremes and large variations.
- Store away from light sources.
- Store in a jewel case, which will hold the disc vertically (Did you know that the little clip in the middle of the jewel case actually holds the disc away from both sides of the case so the recording surface only contacts air?)
- Avoid flexing, bending or scratching, and bringing the disc in contact with dirt, dust and chemicals.
- Never write on the top of a disc with a pencil or ballpoint pen.
What sort of testing is done to disk media to gauge archival longevity? Is this testing actually a reliable determiner, or just a best guess of how to reproduce the effects of time and other contributing factors to data loss?
There is an organization in Switzerland, the International Standards Organization (ISO), which is responsible for developing and publishing standards and tests. They have a special test for determining the life of data on optical media. This test, ISO 1827-2002, is used by media manufacturers to determine data life. The test itself takes approximately 18 months to run and uses cycles of heat and humidity to accelerate aging on recorded discs. This same type of testing has been done for many years to determine the life of photographic prints, for example.
How long can a user expect a standard consumer-grade CD or DVD to reliably hold data (assuming proper care and storage)? How long can a user expect an archival-grade CD or DVD to reliably hold data (assuming proper care and storage)?
Assuming a good initial recording and proper care, consumer grade media can last from one to five years. Professional or industrial-grade media can last from five to 75 years. True archival-grade media, often with a reflective layer of gold, can last 75 to 200 years.
How can a user determine whether the CD/DVD they're buying is archival grade? What information should they look for?
Archival grade media is only made by a few companies, often has a gold reflective layer and is usually identified as such. The Internet is a good source to purchase this media, since the average office store does not carry it.
Well-known brand names are usually not an indication that a disc is archival grade. Many of these companies buy media from several sources and often buy budget media when a manufacturer has an oversupply, and then put their brand name on it. For example, you will often see the HP name on media, but HP does not own or operate any media manufacturing facilities.
If you spend time on Web sites devoted to CD quality, you will start to see some brands consistently appearing at the top of everyone's ratings or quality tests. These companies are Taiyo Yuden, Maxell, Ricoh, TDK, and Verbatim. Taiyo Yuden is what most people who use media for a living will buy. It is very high in quality, very consistent, and has performed very well in the ISO 1827-2002 test.
A branch of the federal government, NIST, is working on universal standards that all media manufacturers will adhere to that will label media with an estimated life. We are at least a year away from that goal.
What is blu-ray technology and what benefits does it bring? What problems might its adoption bring?
A CD can hold up to 700 MB of data. A DVD uses a smaller spot laser and can hold up to 4700 MB or 4.7 GB of data. A blue laser disc uses an even smaller spot laser and should hold up to 25 GB of data on one disc. When each new format comes out it usually is expensive, sometimes making adoption slow. Today, a quality DVD may cost $.75. A blue laser disc will hold five times as much as a DVD, but will probably cost 30 times as much initially. Only people who really need to get all their files on one disc will be able to justify the price premium.
About the Author
Tom Peterson is Product Line Manager for Rimage Corporation, the world’s leading disc publishing company. He is responsible for Rimage's Media Kit program, which includes packaging all media with Rimage printer consumables. Peterson coordinates the purchasing of more than two million CD-Rs and DVD-Rs each month for Rimage. He meets monthly with representatives of all major media manufacturers to keep abreast of changes in technology. Peterson led the initiative within Rimage of working with vendors to establish the Rimage 100-year media warranty.
Do you have other questions about archival media? Ask in the Comments section below.