On Feb 11, 2010, at 2:46 AM, Andrzej Szymanski <szymans@xxxxxxxxxx>
wrote:
> On 2010-02-09 18:15, Fernando Gleiser wrote:
>> Every time we try to copy some large file to the storage-based file
>> system, the disk utilization see-saws up to 100% to several seconds
>> of inactivity, to climb up again to 100% and so forth.
>> Here are a snip from the iostat -kx 1:
>>
>> Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-
>> sz avgqu-sz await svctm %util
>> sdb1 0.00 133811.00 0.00 1889.00 0.00 513660.00
>> 543.84 126.24 65.00 0.47 89.40
>
> The iostat output looks good to me for the RAID setup you have.
> I'd look for the problem in a different place:
>
> note the output of
> cat /proc/sys/vm/dirty_background_ratio
> and try
> echo 1 > /proc/sys/vm/dirty_background_ratio
> whether it helps.
Excellent suggestion, on machines with lots of memory the default
dirty background ratio is way too big, and needs to be tuned down for
both data integrity in the event of a system failure and performance
of the underlying storage configuration.
Take into account the RAID setup, write-back cache size and time it
takes to empty it to disk and pick a dirty background ratio somewhere
in between.
-Ross
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