The burning question

Backing up business-critical data onto CD may not be the fail safe course of action we would like to hope. For how long does a burnt CD last?

While commercially burned CDs containing music or software seem to last forever with care, recordable CDs (CD-R) and read-write discs (CD-RW) have a finite shelf life. Even stored properly with minimal handling, some CDs that are burned on PCs go ‘off’ from around two to seven years, rendering the data unreadable.

As backing up to CDs remains one of the most common ways of storing information among small to micro-sized companies, perhaps it’s time to dig out our old CDs to check? And copying to newer media while we are at it makes sense too.

What this serves to remind us is that media - no matter how great – won’t last forever. And, in some cases with CD-R and CD-RW, as little as two to five years. Magnetic tape is far from dead, and may yet prove to be the safest media for long term secure data storage.

The problem with recordable CDs is in the way the information is committed to the disc. Unlike factory-pressed CDs, which don’t degrade because the data is literally pressed into the disc, recordable CDs use a dye that changes colour or reflectivity when heated. The life expectancy of the CD depends on the particular dye used and whether the disc is one-time (CD-R) or the re-recordable type (CD-RW) which tends to be less stable.

Some estimates put the life expectancy of a properly-burned and stored CD-R at decades. But this is subject to a number of factors, including the quality of the CD recording drive and the speed of the recording.

Low quality or borderline defective drives can ‘under-expose’ the CD during the recording process and so make the data less permanent and stable than it could be. Similarly, the recording speed has an impact too. Fast burners, 52x speed drives, are less likely to produce stable recordings than slower ones.

Keeping to a minimum the amount of handling is also important in preserving data, flexing a disc, for example, causes internal damage. So, too, is how CDs are stored. They should always be individually kept in cases and stored in a cool dry container. Your desk drawer is not a good place.

Be careful how CDs are labelled as the glue from adhesive labels and solvents in marker pens can slowly penetrate the plastic of the disk and destroy the data in the process. For long term storage, it is best to either not label discs but label their case instead or write only on the clear plastic ring in the centre of the disc.