> 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.  Then, when feeding it data that's already gzipped, the hardware 
> compressor is powerless to compress it further, and may expand it a few 
> percentage points with its attempts at compressing data that's already 
> been smunched with gzip.
> 
> The usual cure works like this:
> 
> rewind the tape
> read the header block out to a file with dd
> rewind the tape
> turn the compression off again
> output, using dd, enough data from /dev/zero to cause the drive to have to
> flush its buffers, something in the 2 to 10 meg range should be enough, 
> the point being that you turn the compressor off and don't move the tape 
> until it has to flush its buffers.  At that point, that hidden 
> compression flag will finally be turned off in the tape header.
> rewind the tape again
> Do an amtapetype -f /dev/ice -e 36GB, and copy the resulting size data 
> into your tapetype define in your amanda.conf.
> rewind it again
> dd the tapes label block back onto the tape.
> 
> Do this for each tape that has been used with the compressor turned on, 
> skipping the amtapetype step after the first tape.  And you will of 
> course lose the data on that tape, so its probably a good idea to do this 
> to each tape in the rotation in the hours before it will be re-used 
> again.
> 
> rewind it again.
> run amcheck to see if the label is indeed good, it should be.

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.

> 
> gzip -best can compress some directories to less than 10% of their actual 
> size.
> 
> 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?

> 
> >INFO planner Incremental of server:/srv/samba/profile bumped to level 2.
> >INFO planner server /home 20070404 0 [dumps too big, 15459005 KB,
> >full dump delayed]
> >
> >Amanda is configured to do a full backup each time which is
> >impossible at the moment. I tried to backup ~45 GB of well
> >compressable data. Normally amanda should be able to store the files
> >compressed on the tape.
> >
> >Has anybody some hints for me?
> >
> >   Thanks
> >
> >       Sebastian
> 


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