With all of our recent TTOTD’s recently about variances of audio integrity between different CDR media and burners we’ve begun to get questions about their integrity as a data storage medium in general. One reader writes, “I wonder if there isn’t some checksum-type scheme to maintain the integrity of data written to CDs in this mode? Otherwise wouldn’t there be a lot of numeric errors in other types of data (I envision someone pulling up an archived spreadsheet with corrupted calculations – “Hey look, I owe the IRS $412,032!)?”
Hmm, starts to make you wonder how the IRS stores their stuff. Without getting in to all the minutiae here understand that “regular data” is handled and stored differently than data on an audio disc. In Red Book CD audio there is redundancy though. It is possible to reconstruct some amount of bad data, but as the quantity of bad data goes up over a specific period of time the likelihood of the problem becoming audible goes up. Results are partially dependent upon the type and sophistication of the error correction schemes within the playback device. With regular data the results are substantially more black and white. The redundancy that’s in place allows small amounts of missing or bad data to be completely reconstructed. When it can’t be reconstructed the file almost always becomes corrupt in more substantial ways than a simple digit being off somewhere. So don’t worry about your data in that way. It either will be read and be fine, or it won’t work at all.
The real question is how reliable are the CDR, CD-RW, and DVD media as a long-term storage solution? The answer, in part, is determined by exactly what one means by “long term.” Much testing is still underway, and there appear to be significant differences among different formulations of media (not all of which are predictable), but for keeping data backed up a year or two they seem relatively reliable – at least as reliable as a hard disk. Like any media, it can fail without warning at any time so the only way to really be protected is to have backups of the backups. This rule applies whether you are using AIT, DVD, DLT, or CD-RW.