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GCN Home > 03/08/04 issue

Breaking point

By Joab Jackson, GCN Staff

Optical disks might not last as long as you would expect—or hope

Don’t be mistaken: Optical disks won’t last forever.

Many users think the disks are indestructible, but they are wrong, said Fred Byers, an IT specialist at the National Institute of Standards and Technology.

As the government saves more and more records in electronic format, long-term archiving becomes a puzzle. Paper has lasted for centuries. Can optical disks really last for the 100-year life span envisioned for them?

The good news from NIST is that certain types of optical disks might last that long or even double that—but only if handled with care.

But disk life expectancy depends on many factors, some controllable by users, others not, Byers noted in a disk care guide, NIST Special Publication 500-252.
To test a CD’s endurance, NIST’s Byers ages the disk rapidly in a special environmental chamber.
Image: J. Adam Fenster
To test a CD’s endurance, NIST’s Byers ages the disk rapidly in a special environmental chamber.
The National Archives and Records Administration requested the report, asking NIST to come up with care and handling instructions for optical media. The goal was to imitate a report about magnetic tape care created by the now-defunct National Media Laboratory. Byers said he spent about a year testing disks and working on the guide.

Although many agencies have no archiving policy, they nonetheless are saving a lot of data on optical disks. “There are a lot of questions about the implications of that,” Byers said.

Recordable CDs and DVDs can be as reliable as magnetic tape for backup, he said, and they read much faster because they use random access, whereas users must search files stored on tape sequentially.

The useful life span of optical disks varies with temperature, humidity and day-to-day use. Data degradation at first can go unnoticed because of the error-correcting abilities of disk readers.

NIST has found that recordable disks seem to last much longer than rewritable disks, Byers said, and even longer than manufactured disks such as CDs for installing commercial software.

General industry guidelines now estimate office-burned copies of CDs and DVDs could remain readable for 100 to 200 years.

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