Re: Compression settings on DLT drive

On Wednesday 05 November 2003 06:26, Mike Brodbelt wrote:
>Hi,
>
>I use Amanda to back up to a Quantum DLT 35/70. I used to use
> hardware compression, but am now using software based compression
> on the tape server. I tunr off compression on the drive, but it
> won't stay off, as each night it reads the header from the previous
> backup, and switches back into hardware compressed mode. Can anyone
> give me a simple technique for forcing compression to stay off.....
>
>Thanks,
>
>Mike.

basicly, what you must do is to work outside of amanda to do this.

I don't know how many tapes you have, but I wrote this script a while 
back to do a similar operation.

#!/bin/sh
if [ `whoami` != 'root' ]; then
        echo
        echo "!!!!!!!!!!!!!!!!! Warning !!!!!!!!!!!!!!!!!!"
        echo "fixblock needs to be run by the user root,"
        echo "else the perms on some commands will be denied."
        echo
        exit 1
fi
name=./status

set echo on
# needs a scratch dir to hold temp files
cd /amanda
# blatently stolen from the bash manual
NUMBERS="0 1 2 3"
for number in $NUMBERS
do 
        echo "amtape DailySet1 slot "$number
        su amanda -c 'amtape DailySet1 slot '$number
        mt -f /dev/nst0 rewind
# save the tapes label for amanda, /dev/st0 rewinds
        dd if=/dev/st0 of=./scratch bs=64K count=1
# show the label read
        ls -l ./scratch
        mt -f /dev/nst0 setblk 32768
        mt -f /dev/nst0 defblksize 32768
        mt -f /dev/nst0 compression off
        mt -f /dev/nst0 defcompression -1
# now write label back.  Remove bs and conv if not changing blocksize
        dd if=./scratch of=/dev/nst0 bs=32K conv=sync
# echo current location on tape for your enjoyment
        mt -f /dev/nst0 tell
# Now This _should_ get rid of compressed headers
        echo "forcing buffer flush with an 4+ meg write to tape # "$number
# note use of st0, it rewinds
        dd if=/dev/zero bs=32K count=130 of=/dev/st0 
        echo "Now reading the label"
        dd if=/dev/st0 bs=32K
        mt -f /dev/st0 status
done
exit 0
----------------------------------
Now, if you do not want to run with the larger block size, remove 
those 2 mt lines and the bs options for the dd based usage.

What its doing is turning off the compression, and then forcing a 
buffer flush, which in turn writes the new, non-compressed flags into 
the otherwise hidden tape header.

It works for me :-)

-- 
Cheers, Gene
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Copyright 2003 by Maurice Eugene Heskett, all rights reserved.