Use caution when storing your data

Both business and home computer users have begun to recognize the importance of data redundancy.

Home users may want to ensure they have backup copies of purchased music, financial records and family photos.

Corporate users need to protect critical business data, but they also may need to satisfy record retention and other regulatory requirements.

For the past decade, optical media have been used routinely to archive digital files. Mass production of writable CDs and DVDs has resulted in lower costs and plentiful supply.

However, all media are not equivalent in quality. Even products from a single manufacturer may vary greatly.

Traditional versus writable media

Unlike commercial audio CDs, which are pressed from glass masters, writable media are dye-based. Rather than having physical pits in the matrix material, a CD-R uses a light-sensitive dye layer that changes color density and reflectivity when struck by the drive's laser.

When the CD is read, a layer of reflective material bounces the laser light back to a sensor. Changes in the dye layer result in a modulated light signal that corresponds to the binary data.

CDs and DVDs are often perceived as a permanent storage solution. When faced with dwindling hard drive space, some users will create a data CD then delete files from the drive to free disk space. This may not be such a wise strategy.

In 2003, a Dutch technology magazine reported test results for 30 commercial CD-R brands. Testers had written information to the disks two years prior and then assessed error rates for each of the disks. Incredibly, some of the disks showed significant data loss after only two years of storage.

Their results were not unique. In 2004, the National Institute of Standards and Technology (NIST) published a report on data stability using CDs and DVDs of various compositions.

Although this study subjected the disks to direct light and extremes of temperature and humidity, the results indicated that data stability was largely dependent upon the composition of the disk.

Manufacturers use a variety of dye types, not all of which are stable over long periods of time or when stored under extreme conditions.

NIST researchers concluded that media using phthalocyanine dyes, especially when combined with gold-alloy reflective material, fared much better than typical disks. Unfortunately, the average consumer has no way of knowing the composition just by looking.

A few premium CD manufacturers do offer media labeled as "archival quality," which are tested for long-term dye stability. Unfortunately, premium CDs and DVDs often command a premium price.

Alternative storage

While optical media are cheap and convenient, they shouldn't be relied upon for critical data - at least not as the sole storage strategy. Solid-state "flash" media are becoming an affordable alternative, yet they have not been studied extensively long-term.

RAID-based disk storage provides immediate use and error recovery, but such arrays are not practical for archival purposes.

So, what is the alternative? Large-capacity hard drive prices are dropping rapidly. A one-terabyte external USB drive is currently priced at around $250. A single terabyte drive can store the equivalent of 1,500 CDs or about 200 DVDs.

However, magnetic media are not without problems. Hard drives are sensitive to shock, electromagnetic fields, and controller failure.

Perhaps the best option is to have redundancies. By using high quality disks, creating multiple copies, and storing on varied media, companies can ensure their business continuity, and home users can keep their cherished memories alive for years to come.

Optical disks, especially CD-Rs, are often criticized, as they tend to be used once and thrown away. Over the next 10 years, CDs will likely go the way of the floppy disk, and DVDs may be obsolescent.

In the meantime, it may be worth it to pay a bit more for piece of mind. At least with dye-based media, old data never die - they just fade away.

Monte Kendrick is the president of and principal consultant for Pixelogiq Data Systems LLC, a Madison-based company that offers information security and technology consulting services.