Re: Backup's to DVD
On Mon, 2014-03-17 at 19:11 +0100, Ralf Mardorf wrote:
> On Mon, 2014-03-17 at 18:50 +0100, Ralf Mardorf wrote:
> > On Mon, 2014-03-17 at 17:51 +0200, Lars Noodén wrote:
> > > 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.
> >
> > I made the best experiences with DVD-RAM. _When_ ever it was possible to
> > write to a DVD-RAM the data was safe, _but_ many DVD-RAMs were broken, I
> > payed a lot of money and the new once were already unusable, very often
> > neither Linux nor Windows was able to write data to DVD-RAM or it needed
> > hours just to write 1 KiB. And assumed you never ever will experience
> > writing issues, when using DVD-RAM, what are 4.7 GB good for? How often
> > will you split your tar files?
>
> PS:
>
> Once the data is written, everything is fine. Reading DVD-RAM isn't an
> issue.
>
> DVD-RAM is opto-magnetical. The magnetical layer only could be changed,
> after optical heat allows this. DVD-RAM can be used the way a HDD is
> used, no burning software is needed.
Yes, it's just a rough explanation ;), not a perfect one ;).
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