On Tue, 10 Feb 2009 18:41:53 +0100, Mike Holden <bacula AT mikeholden DOT org>
wrote:
> Foo wrote:
>> Hi,
>>
>> I'm doing a backup on a Debian Etch server which runs a network/time
>> critical app at -20 niceness, but even with nice -n19 bacula-fd still
>> causes glitches (packetloss).
>>
>> They seem to happen when the backup starts and ends, during the backup
>> (doing 20-23 MB/s) there is no problem. An incremental backup that
>> takes 5
>> seconds still causes a glitch, although much smaller. Doing an 'estimate
>> job=servername' via bconsole causes no glitch, but this is probably due
>> to
>> caching after the backup (returns immediately with the correct answer).
>> This makes me think it is disk IO related (2x15K rpm SAS drives in RAID1
>> on Dell Perc/5i - backup goes to other disk array over Gb
>> Ethernet/Fiber).
>>
>> Is there a way to solve this on the Bacula side? The server is normally
>> using only a few percent CPU, with bacula-fd going up to 15-25% at most,
>> it's scheduling, or some disk related holdup that seems to be the
>> problem.
>
> If you suspect disk I/O may be a sticking point, look at using "ionice".
> Works in much the same way as "nice", but for limiting I/O rather than
> cpu.
Thanks, that helped, although there is still some packetloss (about a
quarter of the previous value).
> You could also look at using iotop and iftop to check disk and network
> throughtput at the problem times to see what is going on.
I'm afraid these are too general to troubleshoot the remaining loss, since
they deal with quantity, not quality. Unless the Bacula FD does something
naughty it's probably some low level component that needs optimization (I
can't touch network buffer sizes BTW, which are optimized for the main app
running on the server).
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