On Wed, Apr 04, 2007 at 11:01:20AM +0200, Sebastian Henrich wrote:
> > On Tuesday 03 April 2007, Sebastian Henrich wrote:
> > >Hello,
> > >
> > >I'm using amanda 2.4.5 to backup my server. The tape is a HP DAT 72.
> > >This drives stores 36 GB of uncompressed data. I switched the
> > >hardware compression off and tried to use the software compression.
> > >Now I have the problem that amanda tells me every time
> > >
> > You may be getting bit by something I ran into several years ago now.
> > 
> > If the tape is written with the hardware compression on, then the drive 
> > will detect that and turn the compression on even if you think its turned 
> > off.
...
> 
> I diabled the hardware compression before I used the tapes for the first time 
> like it's described in the docs. mt shows me that hardware compression is off 
> after inserting a tape. So I think that it's really disabled.
> 

The switch may not occur unless the drive actually attempts to read the tape.
Amanda does an initial read before any attempt to write to a tape to check if it
is actually an amanda tape and is the expected amanda tape.

> > Amanda also tracks the amount of compression on a per dle basis, so if you
> > know beforehand the ratio, you can put it in the dumptype spec section to 
> > give amanda a head start on a good guess.
> 
> How can I put the ratio in the dumptype spec?

Can't.  The history of last 3 dumps at full and incremental levels is recorded
in the curinfo file for the DLE after a dump.  I wonder (don't know) if you 
could
clear or edit that file or the relevant lines.

  $ grep comp <curinfo_dir>/<host>/_<DLE>/info
  full-comp: 0.386351 0.386012 0.385504
  incr-comp: 0.196589 0.207102 0.197036
  $

The DLE I ran this sample on shrink to about 38% and 20% of the original size
for full and incremental dumps respectively.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
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