[Bacula-users] LTO speed optimisation

Hi all,

I'd like to try and make some speed improvements to my Bacula setup (5.2.13, Solaris11). I have data (and attribute) spooling enabled using a pool of 46x 1TB directly-attached SAS disks dedicated to this purpose. Data is being despooled to 2x directly-attached SAS LTO6 drives at around 100mB/sec each. I think I should be able to get closer to the ~160mB/s maximum uncompressed thoughput the drives and tape media support (ref: http://docs.oracle.com/cd/E38452_01/en/LTO6_Vol4_E1/LTO6_Vol4_E1.pdf).

I've just done a speed test and can read from the spool array at a sustained 300mB/sec even while other jobs are running, so I'm sure there's no bottleneck at the disk layer. My suspicion is that the bottleneck is at the application layer, probably due to the way I have Bacula configured.

Having read through Bareos' tuning paper (http://www.bareos.org/en/Whitepapers/articles/Speed_Tuning_of_Tape_Drives.html), I've updated the max file size from 1->50GB which increased the throughput from ~75 to ~100mB/sec. I believe I need to look at tuning the block size to gain the last bit of improvement.

Is it still the case in Bacula that changing the Maximum Block Size renders previously used/labelled tapes to become unreadable? I'm up to almost 1,000 tape media already written, so making these unusable for restores without restarting the SD to change configs would be less than ideal. I see Bareos is touting a feature to make changes to block size at the pool level rather than the storage level and so this problem can be avoided by moving newer backups to a different pool while still keeping older backups readable. I haven't seen any reference to this in the Bacula manual; is it something that's already supported or in the plans for a future version?

For reference, this is one of the the relevant drive definitions I'm using, just in case there's something else that would help which I might have missed:
Device {
Name = drive-1-tapestore1
Archive Device = /dev/rmt/1mbn
Device Type = Tape
Media Type = LTO6
AutoChanger = yes
Removable media = yes
Random access = no
Requires Mount = no
Drive Index = 1
Maximum Concurrent Jobs = 3
Maximum Spool Size = 1024G
Maximum File Size = 50G
Autoselect = yes
}

Regards,
Ben Roberts

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