Using mt to try to enable tape drive compression

jeriryan · 06-18-2008, 02:06 PM

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.

AwesomeMachine · 06-19-2008, 09:13 AM

We would need more information about the backup software.

jeriryan · 06-19-2008, 09:52 AM

I'm just using tar to transfer files to a tape drive and I want to enable hardware compression.

marozsas · 06-19-2008, 10:04 AM

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:~>

jeriryan · 06-19-2008, 01:49 PM

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?

jeriryan · 06-19-2008, 02:00 PM

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?

marozsas · 06-19-2008, 02:49 PM

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.

jeriryan · 06-20-2008, 09:49 AM

When I type "mt -f /dev/st0 compression" it says nothing, just goes back to the command prompt.