Le Saturday 11 July 2009 23:34:30, Arno Lehmann a écrit :
> Hello,
>
> 09.07.2009 16:03, Stoyan Petkov wrote:
> > Hello,
> >
> > I've an FD that's making too much iowait on the backed up machine. I
> > tried searching info on the subject but nothing useful comes up. Here is
> > an excerpt from the top utility:
> >
> > top - 18:55:25 up 50 days, 1:48, 23 users, load average: 0.30, 0.32,
> > 0.83 Tasks: 124 total, 1 running, 123 sleeping, 0 stopped, 0 zombie
> > Cpu0 : 2.0%us, 1.0%sy, 0.0%ni, 96.0%id, 0.0%wa, 1.0%hi, 0.0%si,
> > 0.0%st
> > Cpu1 : 2.9%us, 1.0%sy, 0.0%ni, 96.1%id, 0.0%wa, 0.0%hi, 0.0%si,
> > 0.0%st
>
> Unless I'm mistaken, there's not much iowait displayed here. Quite the
> contrary: 96% idle.
>
> > Mem: 1032680k total, 1016456k used, 16224k free, 18468k buffers
> > Swap: 2031608k total, 103044k used, 1928564k free, 645912k cached
> >
> > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
> > 22534 root 20 0 41560 2268 1232 S 6.0 0.2 0:06.32 bacula-fd
> > -c /etc/bacula/bacula-fd.conf
> > 22758 root 20 0 2364 1044 812 R 1.0 0.1 0:01.40 top
> >
> >
> > During normal operation the iowait will stay within 10% limits, however,
> > at some point it jumps to 90-98% and stays that way. I've noticed that
> > even with canceling the job from the director,
>
> Have you tried vmstat, and checked - perhaps using ps - which
> processes do need lots of CPU time when there's so much iowait occuring?
I don't see why having iowait should be a bad thing for a backup application :
iowait is the time the CPU spends waiting for IO (disks...), which should be
most of the time while doing a backup (except if compressing, encrypting, or a
very badly programmed backup application).
There are several reasons why the iowait could raise :
- More IO to be done for a portion of the backup (small files for instance) for
the same volume of data to be sent through the network
- Another application used the CPU during the first part of the backup while
bacula was waiting for IO and has stopped using it (you should go from 100%CPU
to high iowait).
But still I don't see a problem with the FD putting a CPU at 100% IOWait, that
should be normal behaviour.
Anyway, if you really want to investigate this, you could do a strace on FD at
the moment it is at 100% IOWait, then we'll know what it's waiting for :)
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