In the message dated: Tue, 23 Aug 2011 12:01:59 +0200,
The pithy ruminations from =?utf-8?Q?Stefan_Michael_Guenther?= on 
<[Bacula-users] How do I force Bacula to unlock a drive?> were:
=> Hi,
=> 
=> we still have a problem with our tapeloader. 
=> The status of the storage tells me:
=> 
=>  Jobs waiting to reserve a drive:
=>     3608 JobId=1097 wants Pool="Mittwoch" but have Pool="Dienstag" 
nreserve=1 on
=>  drive "Drive-1" (/dev/st0).
=>     3606 JobId=1097 prefers mounted drives, but drive "Drive-1" (/dev/st0) 
has
=>  no Volume.
=>     3608 JobId=1115 wants Pool="Mittwoch" but have Pool="Dienstag" 
nreserve=1 on
=>  drive "Drive-1" (/dev/st0).
=>     3606 JobId=1115 prefers mounted drives, but drive "Drive-1" (/dev/st0) 
has
=>  no Volume.
=> >
=> okay, we had problems with the pool Dienstag and we cancelled the 
corresponding job, but still t
=> he drive is blocked.
=> Hm, neither release, nor unmount or a restart of the storage daemon allows 
me to reactivate the 
=> drive ??
=> 


We've run into what may be the same issue. We've got a SAN-attached tape
library, and 3 HA-clustered servers, any one of which may be the bacual-sd
server.

When bacula-sd halts uncleanly (the daemon is killed, the bacula service
transistions to a different HA node, or the server is shutdown uncleanly),
the SCSI reservation on the tape drive is not released.

The symptom is that bacula and "mtx" are unable to unmount a tape. The mtx
command reports errors like:

        mtx -f /dev/changer unload 28 1
        Unloading drive 1 into Storage Element 28...mtx: Request Sense: Long
        Report=yes
        mtx: Request Sense: Valid Residual=no
        mtx: Request Sense: Error Code=70 (Current)
        mtx: Request Sense: Sense Key=Illegal Request

This seems like a physical problem with the library (ie., the hardware
is unable to eject a tape), but is actually a software issue.

In our case, the tape drive itself gives some diagnostics:

        A host issued a SCSI Prevent/Allow Media Removal command which
        is preventing the drive from unloading a tape cartridge.

Unfortunately, the tape library cannot tell which host (of the 3 possible
bacula-sd servers) issued the lock. The lock is host-specific, and must be
released from the same machine that locked the drive, even if that machine is
not running bacula-sd at the moment.

The solution in our environment is to use the "sg_prevent" command
(from the sg3_utils package) to release the SCSI Prevent/Allow Media
Removal lock:

        sg_prevent --allow --verbose /dev/tape0
        sg_prevent --allow --verbose /dev/tape1

I've put those commands in the bacula-sd init script, to be executed
before the daemon starts, and at shutdown.

Note that bacula-sd must be stopped before running those commands.

I hope this helps.

Mark


=> Stefan
=> 

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