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How To Verify CD-R Data Retention Over Time?
Peter (Professor) Fo writes "I've recently had two CD-Rs reported to me as faulty which are just 3 years old. This is worrying — I suspect the failure rate for this batch could be 10%. When researching CD longevity there is old and unreliable information; pious 'how to cosset your discs so they last 100 years' blurb; and endless discussions of what sort of dye to use, don't use cheap media, burn slower (or don't), but not much by way of hard facts besides there's a lot of data loss going on.
Does anyone know of a generic utility (win or *nix would suit me) that can map sector readability/error rates of CDs? I'd like to measure decay over time in my environment with my media and my other variables; and I expect others would too."
RAID5 for CDs? Is there anything where I can burn 3 CDs with a 'set' of data. When I want to restore my data I just put in each disk sequentially and then it does some RAID5 magic and spits out my data?
Be a cool project, IMHO.
If it's really important, I always verify the integrity no matter what
I do that even if it's not important. I have a script which creates an md5 checksum file for a directory tree and adds it to the directory, and I always run it before burning a CD or DVD. Once burned, I verify the checksum on two different computers.
There have been a few times that the computer that burned the disc successfully verified a new disc, but a different one didn't. When that has happened, I trashed that disc and made a new one.
Sometimes I wonder if a lot of the reports of "deteriorating discs" are actually cases where someone burned a coaster in the first place, and just never happened to try to read or verify the data until years later.
Also looking for Taiyo Yuden brand helps (or anything made in Japan...that should be TY just rebranded). Every knowledgable board I've looked over on the subject has recommended them, and I have never had a single one of their disks out of probably 200 now be bad from the start. Unfortunately I don't have any 'old' disks to test. I keep most of my data backed up on hard drives.
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Exactly. I have 60 archival grade CD-R
s from over 10 years ago that are still readable Yes I have tried them, it is a part of our backup integrity testing every year.
Storage and handling is also very important with them as well.
Do not look at laser with remaining good eye.
I use dvd-ram to archive important files. Designed for archival type storage, the slower media has a 30 year designed life, the faster media has something like 5 year. Add in the builtin ecc and cheap cost, it is a good way to save my source code and photos.
Kindness is the language which the deaf can hear and the blind can see. - Mark Twain
CDs and DVDs will last for a long time, it's the (re-)writable versions that degrade (relatively) rapidly. The non -ROM versions aren't physically stamped, they use dyes that change phase when exposed to lasers. They are very susceptible to damage from UV light (i.e. sunlight), and I believe will deteriorate over time even if stored in a dark room.
The storage footprint of data tends to be inversely proportional to its importance.
People lose sight of this fact, and because they don't see a good way to backup the 500 gigabytes of data they have, they somehow fail to backup the 20 pages of documents that they need to protect their assets or limit their liabilities.
Don't underestimate the value of a document printed in archival ink, stored in several fireproof locations. Definitely don't underestimate the archival value of, and potential longevity of, hand-written journals.
This has worked well for me. I had a situation where a RAID 5 lost two drives and my backup had some corruption in a 100 gig video project. Pulled out my 3 year old DVD's and recovered the data fine (and yes there were one or two of chunks that had problems but recovered from the redundancy).
Just my method and 2 cents.
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