Hard drives life span range is reasonable. Not sure about flash drives.
However, those CD and DVD numbers seem to be off. The only longevity
prediction study out there is the one by Kodak, where the gold metal
layer/phthalocyanine discs showed excellent longevity (greater than 100
years).
I believe good quality CD-R discs with gold metal layer and phthalocyanine
dye would result in that kind of longevity. Other dye/metal layer
combinations will have much less longevity and cheapies possibly failing
within 5 years. All things being equal of course, recording quality, etc.
DVD-Rs because they don't use phthalocyanine dye or gold metal layer would
have a shorter predicted lifetime that "gold" CD-Rs.
I have performed single temperature/RH aging on a wide variety of CDs,
CD-Rs, CD-RWs, DVDs, DVD-Rs, DVD-RWs. This type of study does not provide
estimates of longevity values, but does compare relative stabilities of the
media. A paper will be published soon with detailed results and so I will
not go into too much detail here. The study did show CD-RW and DVD-RW
stabilities well below CD-R (gold metal layer, phthalocyanine dye)
stabilty. I would not recommend erasable media for longevity.
Most of the longevity numbers presented in the literature, magazines, have
no scientific data to support them.
Joe
Steven Smolian
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The March, 2005 issue of Popular Science has a list on page 74:
"Archival Life. These are estimated life spans of standard storage media.
To be safe, transfer your data to new media every few years.
CD/DVD+/-R 2-15 years
CD/DVD+/-RW 25-30 years
Hard drives 3-6 years
Flash drives 10 years"
Without accepting this as gospel but allowing it to provide a sense of
proprtion, the choice among the options they mention seems clear- and that
is bypassing issues concerning how the CD-RW is made and what it is made
of.
I think it fair to state that the consensus here is that external, single
unit storage on an inactive hard drive is poor archival strategy.
Experience has shown that, when faced with limited funds, adminstrators
usually choose to save new data rather than transfer old data.
Preservation through migration requires an inexpensive medium using a
minimum of inexpert labor.
A number of simultaneous alternate possibilities have been raised. Many on
this list are more knowledgeable than I about these other devices and
encloding methods. I, for one, would be quite interested in explainations
of what they are, with a minumum of jargon and with definititions of any
acronyms. I would welcome a sense of the costs of each, advantages and
disadvantages, and informed guesses as to the direction of future cost by
those with experience using these options. An essential facet is data
concerning standards relating to each to avoid future decoding nightmares.
Steve Smolian
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