Dropped interrupts

[Ben Laurie]

Not subscribed to the list, so please cc on replies.

I'm using Bacula with an LTO-2 SCSI drive.

With increasing frequency lately, I've been getting errors like this
from bacula:

backup-sd JobId 13092: Error: block.c:608 Write error at 23:6772 on
device "Ultrium" (/dev/nsa0). ERR=Operation not permitted.

Associated with this, I see in dmesg:

ahc0: Recovery Initiated

[a lot of dump info, including...]

ahc0: Timedout SCBs already complete. Interrupts may not be functioning.

Interrupts must be kinda functioning, because it can go for weeks at a
time without problems.

I've looked into it a bit, and the SCSI board is sharing an interrupt
with one of the USB hubs. My first thought was to configure it to not
use a shared interrupt, but this turns out to be impossible.

Could that be the cause?

Any suggestions on how to fix this? I believe backups are not actually
compromised, but tapes are not filled, which causes some pretty
serious problems.

Obviously happy to provide any more info that would be helpful.