Hello all,
I've just come across a document I wanted to pass along. Please excuse
cross postings. Although I'm a fan of using gold CD's and DVD's for
storage purposes, as opposed to other types of CD's and DVD's, I have to
admit that they are not suitable for all projects and all purposes. I also
have to admit that using them has its own set of challenges and
problems. My mission is to work with people to come up with viable
solutions to their unique data preservation needs. I found the document
below from a link in the Association for Recorded Sound discussion
list. It talks about the risks and implications of using CD's and DVD's
for long term storage. It discusses the need for testing of discs before
and after use, for maintaining redundant copies of data, testing error
levels on an ongoing basis, and migrating to new media. Overall, it's a
very well written document. Worth checking out.
MEMORY OF THE WORLD
PROGRAMME
Sub-Committee on Technology
Risks Associated with the Use of Recordable CDs and DVDs as
Reliable Storage Media in Archival Collections - Strategies and
Alternatives
http://unesdoc.unesco.org/images/0014/001477/147782E.pdf
This got me to thinking on a couple of points, and I'd like your opinion on
them. This could apply to other media as well.
First, redundant data. He recommends a strategy of keeping a Master copy,
a Working copy, and a Safety copy. The Safety copy is stored offsite. He
also recommends that the Master and Safety copies be from different
manufacturers if possible to mitigate potential problems with a particular
formulation.
In other reading I've done, I've heard a slightly different strategy. I
believe this comes from the video environment, although I can't remember
for sure. In this case, you have the Master, Copy Master, and Access
Copy. The Master is only used to make duplicate Copy Masters. The Copy
Masters are used to make duplicate Access copies. The Access copies are
the same as the Working copies above. Thus, the Master is only rarely
accessed, only when a new Copy Master must be made. The Copy Masters are
used as often as necessary to make Access copies for general use. If we
add the Safety master from the above paragraph, that will mean 4 discs are
needed to make each 1 disc of data for the archive.
For those of you that are responsible for collections of digital media of
any type, do you use or recommend a system similar to this? If not, what
would you recommend instead?
The second thing I started thinking about was migration. This has been
discussed on the list before. At some point, either the media will expire
or the technology will change, so the data has to be migrated. Now, the
article above indicates a general need to migrate data within 5-10
years. Do you agree that this would be necessary in so short a time,
assuming the media doesn't fail? How do you plan a budget and logistics
for that? If you are building a new archive, do you start doing migrations
as soon as you finish the original conversions, and just keep working on it
forever, always migrating? That's the way they paint the golden gate
bridge. They start painting. It takes a year to finish. Then they start
again.
Here's something else that occurred to me about migration. I'll make an
analogy from car maintenance (bear with me). I have an SUV. Each tire
costs $180 or so to replace. When they all wear out at about the same
time, that's a $720 repair bill. Ouch! Now, consider a media archive of
10,000 tapes, discs, or whatever. The number is arbitrary. I'm assuming
technological change is somewhat predictable. However, what about the
expiration of the media? Suppose the error rate found during testing on
the media exceeds a safe threshold in 7 years, even though the storage
technology is still viable. It's likely that all the media will start
approaching failure around the same time, just like my tires. Suppose you
had to suddenly migrate 10,000 pieces of media when you didn't expect
to. How do you plan for that as well?
Finally, the article talks about Digital Mass Storage Systems as an
alternative to CD's and DVD's. What has been your experience with such
systems, if you use them? Can anyone recommend specific systems or features?
Sincerely,
Ron
------------------------------
Ron Frazier -- P.O. Box 2284 -- Cumming, GA 30028 -- 770-205-9422
(O) -- 404-431-5472 (C)
Email: rwfrazier AT macdatasecurity DOT com (replace the AT and DOT by hand)
I am an independent consultant interested in exploring ways to archive data
over long periods of time.
Recordable DVD's & CD's can fail in 2-5 years. Don't let that happen to
YOUR data.
Get your GOLD Archival Grade DVD's & CD's from
http://macdatasecurity.com/ today!
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