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The Answer Guy

By James T. Dennis, answerguy@ssc.com
Starshine Technical Services, http://www.starshine.org/

Problems with a SCSI Tape Drive

From Ralf Schiemann on 23 Oct 1998

Hi, I've a problem with backing up our file server (Linux 2.0.33). Attached to the server is a HP C1557A SCSI TapeLoader (6 x 24 GB). Actions on the loader are done without any problems (e.g. loading and unloading of tapes).

But if I try to do a backup via tar (tar cvf /dev/st0 /tmp) the tape display is telling me "Write" and after a short while "Tape Position lost". In /var/log/messages I find the following errors:

kernel: st0: Error with sense data: extra data not valid
Deferred error st09:00: sense key Medium Error
kernel: Additional sense indicates Sequential positioning error
kernel: st0: Error on write filemark.

Can you tell me whats going wrong?? Any help is welcome,
Ralf

I would look at SCSI termination and cabling problems. It sounds like commands are getting through the interface just fine, and streams of data are causing the problem.

You don't say what kernel version nor which SCSI adapter and drivers you're using. If this is a modular kernel, try compiling the appropriate SCSI driver directly into it (to eliminate any chance of anomalies with automatic loading and removal of the SCSI drivers by kerneld, etc).

Try compiling a very minimal kernel with just the drivers you need to do your backup. You want to see if there's some strange conflict between your drivers.

Finally you might try testing this with a different SCSI adapter, with no other peripherals on it and the best cable you can buy. Is this an internal or external unit? I'm guessing external since DAT autochangers are pretty big for internal drive bays).

If you can afford it, it's best to put your SCSI tape drive on a separate SCSI card (a fairly cheap $60 ISA card is fine). This allows you to put the tape drive off that system without having to reboot, and it maximizes performance on the other bus.

Copyright © 1998, James T. Dennis
Published in Linux Gazette Issue 34 November 1998

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