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Hello,
I recommend that you use caution when applying information from a
new fork with relatively young programmers. Bareos recommends
setting the block size to 1M. However, myself, and confirmed by
Quantum for LTO-4 tapes (may change with LTO-5, 6) is that
anything greater than 512K may increase throughput but will
significantly increase errors on dirty drives or old tapes. Thus
you risk losing data.
I currently have a project to ease the problems of changing block
sizes for tapes in Bacula (hopefully by year end). I have not
confirmed, but suspect that if you increase the Maximum Block Size
to 512K, you will be able to read/write new volumes and you will
also be able to read old volumes. I am not sure if read/write of
old volumes would be a good idea though as you would then have a
volume with two block sizes, which should work, but I wouldn't try
it.
I think (and hope) that the only problem you will get into, is
that if you write a volume with 512K blocks, currently, you will
not be able to read it back with a Bacula configured for 64K block
sizes.
If you test and confirm or infirm any of my points, please let us
know.
Best regards,
Kern
On 11/05/2014 12:48 PM, Roberts, Ben wrote:
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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