A/UX: Troubleshooting Tape Backup Problems

Article Change History
----------------------
08/31/92 - REVIEWED
* For technical accuracy.

I haven't been able to back up much of anything. I tried to back up my X11R4
source disk (about 72MB), and "tar" keeps failing on the second tape. I tried:

tar clvbBf 16 72000 - | tcb > /dev/rmt/tc1

and tcb failed with an I/O error after about seven files were written to the
second tape.

I tried:

tar clvBf 72000 - | tcb > /dev/rmt/tc1

and got the same error in the same place.

I also tried:

tar clvbBf 16 72000 /dev/rmt/tc1

This command backed up well into the second tape (but very slowly) and failed
with a memory fault error.

The cmdo dialog for tar (using the tape cartridge) generates a command line:

tar clvbBf 16 4500 /dev/rmt/tc1

which writes only 4500 512-byte blocks to the tape.

Express Tape (a commercial backup product) fails on the third tape, when I try
to back up the root partition.

I noticed the "time slice" parameter has dropped from 60 ticks to 5 ticks. If
I run the "plaid" demo and a few more xdemos, things grind to a halt much more
quickly than in version 1.1. (I have not yet received the A/UX driver that
turns on the cache for the accelerator.)

Can you help?

The first thing we noticed was a minor typo in each of the above command--they
lack the input file(s) or directories. The first one, for example, should have
an input file (/source-tree, for instance) specified in the command line:

tar clvbBf 16 72000 - /source-tree | tcb > /dev/rmt/tc1

We can't reproduce the problem. We used the command below to back up the
entire root (/) directory onto two tape cartridges without any I/O error.

tar clvbBf 16 72000 - / | tcb > /dev/rmt/tc1

The problem with the "tar" command failing on the second tape cartridge may be
bad spots on the second tape cartridge. Try replacing that tape cartridge with
a new one.

The time slice parameter SLICE is set to 5 by default. However, the
kconfig(1M) still states 60. This is an inconsistency. Try adjusting to a
different value to fit your needs.