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Trevor is quite correct. (BTW: John, I'm not talking about your
situation specifically here - just taking the opportunity to jump on a
soapbox...)<br>
<br>
Various studies have shown that
standard CD-R media does *not* in fact have a "nearly infinite" shelf
life, but that the shelf life of the cheap, generic, typically
long-strategy / AZO / cyanine stuff is actually closer to 12 MONTHS.
That's one year. Most floppies last longer than that.<br>
<br>
The top-of-the-line "gold" stuff actually has real gold in the chemical
mixture used to make the burnable layer, which apparently dramatically
improves reliability and longevity - up to about 5 or 6 years so far.
And the quality of recordable media is steadily getting *worse*, not
better. Most major media OEMs now have special "Archival" media that
costs significantly more (approx $3 to $5 per CD) but is "guaranteed"
for rather long periods - like 10 or 25 or 50 years. Keep in mind that
the "guarantee" says they'll replace the media for free if it fails,
they aren't insuring you against data loss!<br>
<br>
Most -RW media is now considered to have a longer data life than the
cheap -R media.<br>
<br>
As to DVD media, the chemical mix required is quite different from CDs,
although CD-RW and DVD-RW are somewhat similar. I'm not aware of any
experimental or epidemiological studies specifically on DVD media,
although various engineering articles have theorized that DVD lifetime
will be approximately 2/3 (66%) as long as CD media of equivalent
quality.<br>
<br>
The claims of "infinite" lifetime all arose from projected lifespans of
factory-pressed CDs, not recordable CDs. A correctly pressed CD
(stored correctly) should still last several hundreds, if not
thousands, of years. Ditto for a correctly pressed DVD. That's
assuming they aren't handled, and don't have any radial stresses placed
upon them. If you laid a stack of CDs sideways so that they were
resting on their edge, those CDs (even factory-pressed CDs) would start
to delaminate beyond the point of readability within 3 or 4 years.
Obviously some are more resistant to radial stresses than others, YMMV.<br>
<br>
Bottom line: don't rely on CD-R, CD-RW, DVD-R, DVD+R, DVD-RAM, DVD-RW,
or DVD+RW media for long-term archival. The only known way to ensure
long-term data archival is to A) use archival-quality media, B) use
archival-quality burners, and C) copy the data to a new generation of
media well within the predicted minimum lifespan for your archival
media. Generally speaking, that means shelling out lots of $$$ for
expensive WORM drives, even more $$$ for the expensive media, and yet
more $$$ for the labour involved to re-copy the data every 5-10 years.
The timespan involved varies greatly depending on how you store the
media.<br>
<br>
Applying those same principles to readily-available CD and DVD burners,
you spend about triple the normal price to get a top-of-the-line burner
(generally Plextor, Pioneer, Panasonic, or Sony but it's almost a
guessing game now), then you spend about 10x the normal price to get
archival-grade media (or at least the "Gold" stuff from Verbatim / TDK
/ Imation / etc. - essentially, get a well-known brand name's top-tier
media), then you store it correctly (laying flat, with pressure evenly
distributed across the surface, no more than about 10 disks in a
stack), then you re-copy it to new media about every 2-3 years.<br>
<br>
If you think this is way too much cost and trouble to keep your data
safe indefinitely, you are probably right. The question is, how much
is your data worth to you? If you're in a federally-regulated industry
(financial, health-care, military, etc.) the fines alone for not being
able to retrieve data could exceed the cost of buying good equipment
and media. If you're running a more "normal" business, you probably
still have financial & taxation records that must be kept for 8
years. And if you're storing stuff like engineering designs, CAD work,
or really any kind of intellectual property, how much do you stand to
lose if you can't prove, for example, prior art in a patent defense
lawsuit? Or if you can't prove you own the copyright to a piece of
work someone else is stealing?<br>
<br>
The good news is that, thanks to the way most of us now store data,
none of this is all that relevant. A lot of CD burning nowadays is
single-use or very short-term only and the media is discarded long
before it is in any danger of becoming unreadable. However, for those
of you that think burning CDs and DVDs is a great way to save your data
"forever", think again.<br>
<br>
-Adam<br>
<br>
<br>
Trevor Cordes wrote:
<blockquote cite="mid200609011849.k81In9Ah028182@pog.tecnopolis.ca"
type="cite">
<pre wrap="">On 1 Sep, John Lange wrote:
</pre>
<blockquote type="cite">
<pre wrap="">For some reason we have a stack of DVDs that must have been burned in
some strange format. When I put one in my DVD drive the drive refuses to
recognize it. When I try to mount it, it simply says "no media".
</pre>
</blockquote>
<pre wrap=""><!---->
My guess is you're screwed. The problem is probably not that the OS
can't understand the format, it's that the drive itself can't figure it
out. It was most likely a failed burn, dying burner, not fixated or
something like that.
I verify all burns immediately after burning for full read verification.
Good habit to get into.
Also, high-end Verbatim (or other noteworthy brand like Imation)
data-life-plus media is recommended for anything important. It's not
too much more money for peace of mind. There really is a difference in
quality. I can order them in at good prices if anyone's interested.
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</pre>
</blockquote>
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