Digital archiving tools

Alexander Schreiber als at thangorodrim.de
Sat Mar 12 17:53:49 CST 2011


On Sat, Mar 12, 2011 at 02:53:54PM -0500, Teo Zenios wrote:
> I have used DDS DAT for years, currently trying out DLT and AIT2

*eek*

DDS tapes are _not_ a reliable backup medium, quite the opposite, they
can be a perfectly valid excuse why some annoying data has be "lost".

In a previous job, we used DDS3 tapes for boot & install (Ignite-UX tapes).
We always kept three copies of each tape and despite rarely using them
(well, how often do you reinstall a Unix production or even staging
server?) and the low machine count (IIRC < 10 machines) I aquired a
stack of  10 or 15 dead (== read errors) tapes in 2 years in that job.

As a contrast, the SDLT library had some 20 or so tapes in it, with regular
use (it being _the_ backup storage system) and it rejected (due to read errors
IIRC < 5 tapes in that same time.

In fact, from what I've seen, DDS tapes should be considered suspect
after 10-20 cycles (load/unload/read/write) and considered junk after
30-40 cycles. Plus there is the charming habit of some HP DDS drives to
very slowly drift out of alignment. So you can read the current and last
few generations of backup tapes on that drive but should it ever die ...

> drives (nice to have a 50GB native tape). While I have 100's of
> burnt CDs that are 15 years old by now, I don't think DVDr will be
> as good. And I still mess around with MO drives for my old gear,
> picked up a few more drives in the last year incase mine fail.

My MO drive unfortunately died, so I'm on the (low priority) lookout 
for a replacement. But these days, my backups go either onto DLT-III(XT)
(10/15 GB native) or LTO1 (100 GB native) backup tapes. Both are linear
recording (as opposed to the helical recording of DDS) tape systems and
both are specced to keep their data intact for 20+ years and 500+ cycles
given proper storage.

Another backup medium I use is DVD-RAM, which sounds reasonably promising
as a backup storage medium, plus you can put a filesystem on it and run
r/w operations, simplifying access.

Kind regards,
           Alex.
-- 
"Opportunity is missed by most people because it is dressed in overalls and
 looks like work."                                      -- Thomas A. Edison



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