[RndTbl] Problem Reading DVDs

[Adam Thompson]

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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