[Bacula-users] Unable to read tapes after changing maximum block size

Dear List,

after increasing Maximum block size to 516096 I find that I am unable to
restore data from my backup, although the backup job itself ran fine.

The corresponding error message:

30-Mai 14:47 debian-sd JobId 1959: Warning: acquire.c:265 Read acquire:
Requested Volume "000006L3" on "LTO" (/dev/nst0) is not a Bacula labeled
Volume, because: ERR=block.c:275 Volume data error at 0:0! Wanted ID:
"BB02", got "UUUU". Buffer discarded.

A bit of background: we are using an HP 1x8 G2 Autoloader with one
Ultrium-3 drive. The Unit is attached via SCSI, the loader is equipped
with a barcode reader.

We are running bacula-5.0.2 from Debian Squeeze (32 bit).

The reason to increase the max block size was that we observed bad
performance and bad fill rates on despooling.

We are despooling data from a LVM-stripset with 3 disks. With the
default block size we frequently saw write rates (to the tape) as low as
20MB/sec. Also, in those cases, the tapes would report 'Full' with just
about 200GB written to the tape instead of the ~400GB we used to see.

With the increased block size the despool speed is up to ~55 MB/sec and
the tapes are again holding the expected ~400GB of data.

In retrospect the problem (slow writes) has started to occur after
flashing loader and tape up to the latest firmware. This was done
because we were experiencing problems with the autoloader robotics
(which have disappeared with the updated firmware).

The btape test ran without any problems with the increased block size.

Any pointers would be greatly appreciated.

kind regards,
Nils


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