[Bacula-users] [semi-solved] LTO-4 tape: only 20mb/sec when used with bacula
2010-06-21 05:59:47
Am Montag, den 21.06.2010, 01:20 +0200 schrieb Lukas Kolbe:
> Thanks for the hints. Changing the block sizes to the ones you mentioned
> doesn't help unfortunatly.
>
> Maybe it is a completely different problem: The backups are made to the
> diskpool in parallel, from a few different clients. The SD writes them
> to disk with about 200MiB/second as a whole and from 5 to 50 MiB/second
> per job. That means that a single job is fragmented in many Volumes.
>
> I've just activated data spooling for the copy job, and even the
> spooling process doesn't get faster than 20MiB/second while still
> consuming one full cpu-core.
>
> The volume size is 32GiB if that matters (I don't want to have too many
> files in the diskpool).
>
> I have no idea why bacula-sd consumes so much cpu-time and obviously
> limits the throughput here.
Okay, I have to correct the 20MiB/sec figure for the tape drive. After I
activated Data Spooling for the copy job, I installed sysstat and saw
this:
01:10:01 AM tps rtps wtps bread/s bwrtn/s
01:20:01 AM 716.75 253.16 463.59 64086.25 7226.24
01:30:02 AM 494.51 166.13 328.38 42533.10 5090.18
01:40:01 AM 308.48 142.18 166.30 36369.89 2565.75
01:50:01 AM 301.74 127.34 174.39 32536.13 2694.53
02:00:01 AM 306.21 125.27 180.94 31923.61 2791.23
02:10:01 AM 403.41 147.37 256.04 37593.61 3979.05
the sd reads the volumes from disk with 20-30MiB yet writes to the spool
with only 1.5 to 4MiB/sec. This night he got a whopping 33GiB into the
spool.
For comparison, I dd'ed a volume to /dev/null while the copy job was
running:
[root@shepherd ~]# dd if=/var/bacula/dp/fs1/Vol0070 of=/dev/null bs=1M
9175040000 bytes (9.2 GB) copied, 12.0225 seconds, 763 MB/s
But dd'ing it to another file reveals a problem with the storage
subsystem I believe:
[root@shepherd ~]# dd if=/var/bacula/dp/fs1/Vol0070 of=/var/bacula/dp/fs2/xxx
bs=1M
849346560 bytes (849 MB) copied, 32.665 seconds, 26.0 MB/s
- and dd is also consuming one full core while doing this.
Both filesystems are LVM-Volumes with ext4 on the same RAID-Array on an
Adaptec 52445. This just shouldn't happen. I'll report back when I find
a solution to this problem, thanks for your patience and sorry for
accusing bacula-sd of being at fault here!
--
Lukas
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