On Friday 24 January 2003 05:31, Harri Haataja wrote:
>On Wed, Jan 22, 2003 at 01:55:32PM -0500, Gene Heskett wrote:
>> On Wednesday 22 January 2003 09:05, hochenaw wrote:
>> >we have an HP Surestore dlt vs80e and use hp dlt IV tapes
>> > (capacity 40/80GB) under linux.
>
>...
>
>> >How can i activate software or hardware compression (cant find
>> > an entry in amanda.conf, just Client or Servers best in
>> > dumptypes-file)?
>>
>> Hardware depends on the os in use. Some os's have a choice of
>> compressed or uncompressed drives in the device list and will
>> turn the drives compression on and off according to the
>> devicename you used to address it. Linux does not however, so
>> one must find the switch setting on the drive itself that turns
>> this on/off.
>
>...
>
>> Off is the generally recommended hardware setting for use with
>> amanda because if the machines have the horsepower to do their
>> own compressing, they can often beat the hardware compression by
>> quite useable amounts, thereby putting more on the tape than the
>> hardware compressor can.
>
>...
>
>I use this in my /etc/modules.conf on Linux:
>post-install st mt datcomp off
>
>Which uses mt to switch off compression every time the module
> loader autoloads the scsi tape driver.
Unforch, this also doesn't actually do any good if the tape itself
has ever been written to with the compressor turned on.
The tape is scanned by the drive to see what it is, and if it finds
the compression turned on in the tapes hidden header, the drive
will turn it on despite your wishes. To convert a once written in
compressed mode tape to an uncompressed tape takes a bit of fooling
around with dd and mt.
First, rewind the tape
dd the amanda header out to a scratch file
rewind the tape again
use mt to turn off all the compression stuffs, thre are about 3
ways.
use dd to write about 10 megs worth of /dev/zero to /dev/st0
dd the amanda header back to the tape which was rewound by your use
of /dev/st0 above.
This 10 meg write forces the drive to flush its buffers to the media
while the compression is turned off, thereby resetting that flag in
its hidden header.
--
Cheers, Gene
AMD K6-III@500mhz 320M
Athlon1600XP@1400mhz 512M
99.22% setiathome rank, not too shabby for a WV hillbilly
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