Tape drive problems

["J" <sundiver discordia org>]

I have a DSS tape drive connected to a UDB. I can read and write
test files to and from it just fine. I have a backup script that runs
each night which uses tar to dump a bunch of file systems to tape.
After the backup runs for a while, I get...

tar: Cannot write to /dev/tape: Input/output error
tar: Error is not recoverable: exiting now

Thinking there was a problem with the tape drive, I got another one
(similar, but not exaclty the same model) and some new tapes. And it does
exaclty the same thing. I'm not running out of space on the tape and I
have used a cleaning tape on the drives. So now I'm wondering if there is
some bug in the tape driver or tar. Has anyone seen something like this?
And is there a way to get more error information that just Input/output
error?

The details...

166Mhz UDB
Redhat 5.1
Kernel 2.0.35
Tape drive:
  Host: scsi0 Channel: 00 Id: 05 Lun: 00
    Vendor: ARCHIVE  Model: Python 28388-XXX Rev: 4.98
    Type:   Sequential-Access                ANSI SCSI revision: 02

Backup script:
mt -f /dev/tape rewind
mt -f /dev/tape datcompression 1
mt -f /dev/tape status
date > /dev/tape
cat /etc/fstab > /dev/tape
awk '{ if ($3=="ext2") { cmd = "echo " $2 "> /dev/tape ; tar clf /dev/tape
" $2; print cmd; system(cmd)}}' < /etc/fstab
date > /dev/tape
mt -f /dev/tape rewind
mt -f /dev/tape status
mt -f /dev/tape offline

Results from backup script:
Compression on.
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 512 bytes. Density code 0x13 (DDS (61000 bpi)).
Soft error count since last status=0
General status bits on (41010000):
BOT ONLINE IM_REP_EN
echo /> /dev/tape ; tar clf /dev/tape /
tar: Removing leading `/' from absolute path names in the archive
tar: Removing leading `/' from absolute links
echo /usr> /dev/tape ; tar clf /dev/tape /usr
tar: Removing leading `/' from absolute path names in the archive
tar: Removing leading `/' from absolute links
tar: Cannot write to /dev/tape: Input/output error
tar: Error is not recoverable: exiting now
echo /var> /dev/tape ; tar clf /dev/tape /var
tar: Removing leading `/' from absolute path names in the archive
tar: Cannot write to /dev/tape: Input/output error
tar: Error is not recoverable: exiting now
...


So, does anyone have any ideas? Please help, before I go insane trying
to figure this out.

- J