On Wed, 23 Oct 2002 at 5:10pm, Joseph Sirucka wrote
> I would like to know where and what do I insert into the amanda.conf for
> allow tape compression to work.
>
> the tape unit is a hp1537A in a six stacker based unit.
That depends on your OS and how the tape drive does compression.
Sometimes, it is done by using a specific tape device, e.g. /dev/rmt/0cn
on Solaris ("c" for compress). The tape device you would specify in your
amanda.conf.
Sometimes it is done via mt commanda, e.g. 'mt -f /dev/nst1 compression 1'
for my AIT1 drive on Linux. This I put in the script that runs my nightly
backups.
Finally, if you want to use hardware compression (and that's not
necessarily a bad thing (although some would argue otherwise)), you need
to a) make sure that you're not also using software compression and b) lie
to AMANDA about how big your tapes are. This lie (in the length parameter
of your tapetype) is based on a guess of how compressible your data is and
how well the drive compression works. It will probably take some
finangling to optimize -- guess too big, and you'll hit EOT every night;
guess too small and you'll be wasting tape. It is, in part, this
guesswork that makes some people strongly recommend software compression,
in which AMANDA keeps a history of how compressible your data is and you
don't have to lie to AMANDA about your tape size. Of course, if you can't
spare the cycles, then hardware compression will work just fine.
--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University
