[Gllug] re: backups

[t.clarke]

What, realistically, is the safe life of a DVD-R disc?
I understand that DVD-RW discs naturally have a shorter life, but I got the
impression from various web pages that DVD-Rs are rated at 100 years archive
life.   Whilst this may seem optimistic, it would seem that DVD-Rs should be
a good choice for archiving large amounts of 'static' data.  They are also
dirt-cheap, if you stock the the 4Gig variety.

Am I correct in understanding that to write a DVD-R you need to first assemble
the complete disc-image on a 'filesystem-file' on disc and then splat the whole
thing at the DVD in one fell swoop?  In which case, one small constraint on
using DVDs would be the need to have spare hard-disc space.

With regard to compression of mail archives, I guess if you were to tar off
a modest number of files indvidually and then compress, prior to then taring
the compressed tars, you would at least wouldn't lose the lot if an area of
archive media goes bad (assuming you can skip it!).  Having said that, I was
under the impression that modern tape systems (including DAT) have pretty
good error-correction techniques to avoid the problems of occasionally bad
media patches.  I guess if the data is that valuable you back it up several
times on different media by different methods, and then keep the backups in
different places!

Tim

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