[RndTbl] Problem Reading DVDs
athompso at athompso.net
Fri Sep 1 22:59:25 CDT 2006
Trevor is quite correct. (BTW: John, I'm not talking about your
situation specifically here - just taking the opportunity to jump on a
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
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.
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.
> Roundtable mailing list
> Roundtable at muug.mb.ca
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