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Old 06-18-2008, 02:06 PM   #1
jeriryan
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Using mt to try to enable tape drive compression


Hi all,

When I type
Code:
mt -f /dev/st0 compression X
, where X is any gibberish like 1, 1000000 or bobgoestoboise, it gives me no feedback to know what happened, just goes back to command prompt. How do I know if compression is on or off or what? I do however get feedback when X is -1, where it says
Code:
mt: negative repeat count
. No idea what that means.
 
Old 06-19-2008, 09:13 AM   #2
AwesomeMachine
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We would need more information about the backup software.
 
Old 06-19-2008, 09:52 AM   #3
jeriryan
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I'm just using tar to transfer files to a tape drive and I want to enable hardware compression.
 
Old 06-19-2008, 10:04 AM   #4
marozsas
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On a openSuSe 10.2, as root user, and on a SCSI DAT tape drive, "mt datcompression" without arguments returns the current compression mode:
Code:
root@bigslam:~> mt -f /dev/st0 datcompression
Compression off.
mt: /dev/st0: No medium found
root@bigslam:~>
 
Old 06-19-2008, 01:49 PM   #5
jeriryan
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I don't know if it's RedHat or if I have an old version of the program, but when I type
mt -f /dev/st0 datcompression
it says mt: unknown command "datcompression".

Any ideas?
 
Old 06-19-2008, 02:00 PM   #6
jeriryan
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In the man pages for mt it says: The compression within the drive can be switched on or off using the MTCOMPRESSION ioctl. I have no idea what this means. Can someone explain?
 
Old 06-19-2008, 02:49 PM   #7
marozsas
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ioctl is a system call to the driver which knows about the device itself. There is a iocl named MTCOMPRESSION, that's it.

I think on a RH system the right parameter for "mt" is just "compression", not "datcompression" as is in openSuse.
try "mt -f /dev/st0 compression" without any additional parameters to query the device.
 
Old 06-20-2008, 09:49 AM   #8
jeriryan
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When I type "mt -f /dev/st0 compression" it says nothing, just goes back to the command prompt.
 
  


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