The CD life span

Over the holidays, I took some time out to clear up the mass of recordable CDs lying around all over the office. As part of the exercise, I tested each to see whether the contents matched the labels. There were a few surprises.

Pleasantly, I discovered an audio CD thatI had given up for lost, but that had just been put back in the wrong case. Not so pleasant was the fact that a nasty little proportion of the backup CDs had errors.

No key data was lost -- just personal stuff from many years ago that happens to be backed up onto tape (I think) -- but it was a timely prod about the reliability of certain types of recorded media.

Then I read in Computerworld that an IBM storage expert reckons that some types of burned CDs will last for only two to five years. Interestingly, I found that the very old backup CDs I burned over 10 years ago were fine, but that the few that were not were about five years old.

One of the possible reasons for that is the older batch were burned at 2x in my old trusty HP recorder (which has since gone to the great CD burning vault in the sky) but that the newer ones were recorded at whatever the drive could handle -- 20x, 32x and sometimes 48x.

Kurt Gerecke, the aforementioned storage expert, says that, unlike pressed original CDs, "burned CDs have a relatively short life span of between two to five years, depending on the quality of the CD. There are a few things you can do to extend the life of a burned CD, like keeping the disc in a cool, dark, space, but not a whole lot more."

There is a fairly important distinction between write once (-R) and read/write (R/W) CDs that the article does not cover (in case you were about to rush out and buy yourself a DLT).

On a CD-R, the data layer sits below the reflective layer and it is the one that is burned permanently. CD-R/W discs have a metallic layer that is heated at different rates to produce different spots that can be interpreted by a laser as being a 0 or a 1.

In feedback on this article, someone complained that Computerworld was unfairly comparing the permanent process of a CD-R with the rather less permanent one of a CD-R/W. To confuse things even more, the situation is reversed with DVDs. Read-write DVDs apparently last longer than the write-once variety, because of the metal alloys used.

What about the environment? Well this office is certainly a cool, dark place, so no worries there. Perhaps I could just move everything onto hard drives? Not so fast, cautions Gerecke. Hard drives are not perfect either. If the disk bearing is an el cheapo, then your precious data is also at risk. The most reliable backup medium seems to be magnetic tape, which has a life span of 30 to 100 years if kept properly.

All of this is somewhat worrying. To be sure, I have no backup and storage problems now, but I am concerned that in the next three to five years, I will have to make sure that tape backup is used for practically everything here.

And here is a first for this column: a price request. If you resell DLTs or SDLTs, preferably 160GB or more, drop me a line please. And, if I have been wrong about CDs, drop me a line too.

I have clients out there in other government departments who depend on CD and DVD backup for auditing purposes, and I do not need complaints about lost data from three to five years ago.

Charl Bergkamp is an overworked, underpaid systems support engineer in the Lambda Bureau, the ICT department of the Ministry of Boards, Committees and Working Groups. He would love to hear from kindred spirits in the ICT corporate world. Send tip-offs, hints and blatant accusations to charl.bergkamp@gmail.com.

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