Re: Backup's to DVD
On 03/17/2014 05:06 PM, Steve Litt of Troubleshooters.Com wrote:
...
> So far, I haven't had readability problems on old CDs and DVDs.
> Blu-Rays seem a little squirrelly over time, but CDs and DVDs seem
> readable for many years.
...
> 3) Magnetic disks can be (accidentally) erased. Not so with write-once
> optical media.
...
CDs and DVDs are physically different media than CD R and DVD R which
are in turn different from CD RW and DVD RW. CDs will last a long time,
as they have a layer of physically dented metal between slabs of
plastic. But you can't press one yourself. For anecdotes, I have some
pushing 30 years that play but I don't have MD5 checksums or anything to
verify them.
I've had some CD R last only a few years, starting from the date of
manufacture not date of burn. The claim is 5 to 10 years, from date of
manufacture, but I have yet to see a date on the packages. CD R uses a
layer of dye which is then burned opaque. Those with higher quality
dyes should last longer before data loss begins but the dyes oxidize
over time and the rate depends on storage conditions and atmosphere.
About the only advantage is that they cannot be re-written so, while
they last, can serve as proof or evidence if a proper chain of custody
is also maintained.
CD RW is more complex having a phase-changing layer but max out at a
theoretical 25 years under ideal storage and handling conditions,
starting from quality manufacturing.
See:
http://www.clir.org/pubs/reports/pub121/sec4.html
The longevity of flash is still a big unknown.
Regards,
/Lars
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