Jon LaBadie wrote:
> 
> On Wed, Aug 07, 2002 at 02:46:21PM -0700, Paul G. Allen wrote:
> > My changer has an HP35480A DAT drive. Should I enable drive compression
> > for use with Amanda and NOT use software compression for backups, or
> > should I disable the drive compression and use software compression for
> > backups? The compression on these drives is enabled/disabled with DIP
> > switches. It can be controlled through software, IF the SCSI driver
> > supports it and it looks like scsi-changer does not (I have no
> > indication that I am able to turn the drive compression on/off, even
> > though the DIP switches are currently set to allow it).
> 
> Actually, the DIP switch options are what state it "powers up to" and
> "whether" it can be changed by software.
> 
> Think of the changer and the drive as two seperate "devices".
> The changer doesn't deal with compression, so scsi-changer doesn't either.
> 
> How you change compression settings is OS and driver dependant.  Common
> ways are through device names (eg. solaris had drive 0l and 0c type names
> showing "l"ow density and "c"ompressed density) and by mt(1) command line
> arguments (eg. I think linux uses this).
> 

Yes, Linux uses the "compression" or "defcompression" options to
enable/disable it with mt. The drive has two DIP switches for setting it
to enabled, disabled, and enabled w/software control. It is set for the
later, but the documentation states that whether or not software can
turn it on/off is system dependant. There seems to be no indication from
mt whether the command is working or not, but in my initialization and
reset scripts I use mt to turn compression off. We'll see what happens.

Incidently, xinetd still does not work. I did enable SCSI disconnection
on the drive and changed the tapetype a little as per the Amanda FAQ.
The current backup is running better and the system is usable during
backup since the SCSI bus is not being hung while waiting for the tape
drive to complete commands.

PGA
-- 
Paul G. Allen
Owner, Sr. Engineer, Security Specialist
Random Logic/Dream Park
www.randomlogic.com