On Fri, May 29, 2015 at 4:18 PM, Gregory Farnum <greg@xxxxxxxxxxx> wrote:
> On Fri, May 29, 2015 at 2:47 PM, Samuel Just <sjust@xxxxxxxxxx> wrote:
> > Many people have reported that they need to lower the osd recovery config options to minimize the impact of recovery on client io. We are talking about changing the defaults as follows:
> >
> > osd_max_backfills to 1 (from 10)
> > osd_recovery_max_active to 3 (from 15)
> > osd_recovery_op_priority to 1 (from 10)
> > osd_recovery_max_single_start to 1 (from 5)
>
> I'm under the (possibly erroneous) impression that reducing the number of max backfills doesn't actually reduce recovery speed much (but will reduce memory use), but that dropping the op priority can. I'd rather we make users manually adjust values which can have a material impact on their data safety, even if most of them choose to do so.
>
> After all, even under our worst behavior we're still doing a lot better than a resilvering RAID array. ;) -Greg
> --
Greg,
When we set...
osd recovery max active = 1
osd max backfills = 1
We see rebalance times go down by more than half and client write performance increase significantly while rebalancing. We initially played with these settings to improve client IO expecting recovery time to get worse, but we got a 2-for-1.
This was with firefly using replication, downing an entire node with lots of SAS drives. We left osd_recovery_threads, osd_recovery_op_priority, and osd_recovery_max_single_start default.
We dropped osd_recovery_max_active and osd_max_backfills together. If you're right, do you think osd_recovery_max_active=1 is primary reason for the improvement? (higher osd_max_backfills helps recovery time with erasure coding.)
-Paul
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