Infant mortality and longevity of DVD media?
Watzman at neo.rr.com
Sat Oct 6 08:49:39 CDT 2007
First, I don't think that DVD media is subject to "infant mortality" at all,
which is not to say that a just burned disc can't be defective. Now a
couple of things that look like infant mortality are possible, although the
mechanisms are not the same as what we usually call infant mortality. One
of these is that data written a burner whose laser power is below spec can
"fade" over time, but this is mostly a problem when using "RW" media (which
should be avoided for archival and backup uses). Also, a media that is
subject to bending can delaminate .... DVDs are a sandwich of two layers of
plastic glued together, and the data is stored on a dye layer coating on the
inside, at the juncture of the two layers. Delamination is fatal to the
data, and normally occurs from the outside in .... Good advice is to only
use 80% to 90% of the media capacity, leaving the outside edge (which is
where the first damage usually occurs) unused for data anyway.
Second, there is no doubt, I don't think, that dual layer media is
considerably less reliable than single layer media (knowing how dual layer
works, it's hard to believe that it works at all). That said, I have not
yet had a problem with any of the dual layer backups that I've made.
The subject of optical media longevity is one of considerable debate. All
studies by the media makers suggest a life of several decades to centuries,
but some skeptics insist on saying less than 10 years. I have optical CD
media that is now 12 years old that I can still read just fine. I think
that some of your practices are excessively conservative (such as only
applying power when the drives are being used), but will do no harm. The
biggest risk, I think, is burning with a marginal burner (low laser power
and/or bad or just dirty optics). Reading the media with a variety of
drives other than the one used for burning is certainly not a bad idea, but
for most users is unacceptably time consuming.
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