Trevor is quite correct.  (BTW: John, I'm not talking about your situation specifically here - just taking the opportunity to jump on a soapbox...)

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.

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!

Most -RW media is now considered to have a longer data life than the cheap -R media.

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.

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.

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.

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.

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?

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.

-Adam


Trevor Cordes wrote: 
On  1 Sep, John Lange wrote:
  
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".
    

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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