"Olaf Seidel" <[EMAIL PROTECTED]> writes:
> Hi,
>
> how do I use hardware compression of the tape drive? I used
> "compress none" in amanda.conf and set up compression for the
> tape with "mt -f /dev/nst0 compression on". But the Amanda mail
> report announced, that there was no compression. I've got a tape
> length of 23616 meg (as tapetype said for a compressed 50gig
> OnStream ADR50). The backup was about 6721 meg and tape
> usage was 28,5%. I've run tapetype with hardware compression off
> ("mt -f /dev/nst0 compression off"), like the manual said. Where is
> the mistake?
Olaf,
Amanda can not "see" hardware compression. So Amanda can't really
figure out how much data fit's on a tape.
If you set a tape type without hardware compression Amanda AFIK does
not use the space gained by compression. If you set a tape type with
hardware compression you bet on a certain compression ratio of
e. g. 1:1.5 . If you add a lot of uncompressable data (e. g. pictures,
MP3's) you run out of tape.
I'd recommend to let amanda clients do the compression and to switch
hardware compression off. Or you can go for the increased safety and
speed of not using compression at all. The problem with compression is
a bit flipping somewhere on tape: AFAIK tar.gz and dump tape "files"
are not readable behind the block with the switched bit.
Johannes Niess
--JAA13530.975659970/server.landtechnik.uni-bonn.de--
