From: Aron Roberts (aron_at_socrates.berkeley.edu)
Date: Thu Sep 18 2003 - 12:57:21 PDT
At 10:38 -0700 2003-09-18, Rusty Wright wrote:
>Is anyone using rewritable dvd discs as data discs (not video) for
>backing up their files? Someone in a newsgroup is saying that
>rewritable discs are too unreliable for backups.
There are at least two issues: whether optical media -- e.g. CD-R,
CD-RW, and the various write-once and re-writeable DVD formats -- are
reliable for data backups in the short run, and whether these backups
will still be usable after being stored for many years.
Below are links to a few random articles on these general topics.
Some points quickly gleaned from scanning these:
- Most articles have focused on CD-Rs, not the various DVD formats.
- Some state that the theoretical life of data on optical media is
in the 80-100 year range, but since this media has been in
practical use for only about 15 years, this is pure speculation.
(Various tests can simulate longer aging, but are by no means exact.)
However, at least one set of tests showed that *some* CD-Rs "were
already unreadable after twenty months." (More below ...)
- The characteristics of the coating (lacquer or otherwise) on the *top*
surface of the media may be an important factor in data longevity,
as well as the dye used and the metal used in the reflective layer.
- Due to different physical characteristics, re-writeable media
may be less suitable for long-term backup than write-once media.
- Storage conditions are also an important factor.
- The speed at which data is written to the media may have at least
a minor impact on data integrity, and 'slower is not always better.'
- The presence of certain types of errors can be used to help
identify media that is about to go bad.
- Overall, optical media is likely to be more reliable than magnetic
tape.
"Say Goodbye to Your CD-Rs in Two Years?"
http://slashdot.org/article.pl?sid=03/08/24/1253248
>Little Hamster writes "According to an article on cdfreaks.com, a
>test done by the Dutch PC-Active magazine showed that among 30
>different CD-R brands tested, a lot of them were already unreadable
>after twenty months.
(A typically lively and occasionally informative Slashdot discussion
ensued ...)
Fred Langa
"Is Your Data Disappearing?
Backup tapes can go bad in as little as a year or two. What about CD-Rs?"
Information Week, July 23, 2001
http://www.informationweek.com/story/IWK20010719S0003
Tim Au Yeung
"Re: CD Quality and Longevity"
http://library.wustl.edu/~listmgr/imagelib/May2002/0028.html
Includes some useful, common sense recommendations at the end.
Digital Equipment Review
"Data Storage and CD-R Longevity"
http://www.beauphoto.com/frames/digital/news/cdr.html
Chip Chapin
"Is It Better To Record At Slower Speeds?"
http://www.chipchapin.com/CDMedia/art-recspeed.php3
Jerome L. Hartke
"Measures of CD-R Longevity"
http://www.mscience.com/longev.html
Aron Roberts
Workstation Software Support Group
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