FYI in my test I used osd_max_backfills = 10 which is hammer default. Post hammer it's been changed to 1.
Thanks & Regards Somnath -----Original Message----- From: Christian Balzer [mailto:ch...@gol.com] Sent: Thursday, May 12, 2016 10:40 PM To: Scottix Cc: Somnath Roy; ceph-users@lists.ceph.com; Nick Fisk Subject: Re: [ceph-users] Weighted Priority Queue testing Hello, On Thu, 12 May 2016 15:41:13 +0000 Scottix wrote: > We have run into this same scenarios in terms of the long tail taking > much longer on recovery than the initial. > > Either time we are adding osd or an osd get taken down. At first we > have max-backfill set to 1 so it doesn't kill the cluster with io. As > time passes by the single osd is performing the backfill. So we are > gradually increasing the max-backfill up to 10 to reduce the amount of > time it needs to recover fully. I know there are a few other factors > at play here but for us we tend to do this procedure every time. > Yeah, as I wrote in my original mail "This becomes even more obvious when backfills and recovery settings are lowered". However my test cluster is at the default values, so it starts with a (much too big) bang and ends with a whimper, not because it's throttled but simply because there are so few PGs/OSDs to choose from. Or so it seems, purely from observation. Christian > On Wed, May 11, 2016 at 6:29 PM Christian Balzer <ch...@gol.com> wrote: > > > On Wed, 11 May 2016 16:10:06 +0000 Somnath Roy wrote: > > > > > I bumped up the backfill/recovery settings to match up Hammer. It > > > is probably unlikely that long tail latency is a parallelism > > > issue. If so, entire recovery would be suffering not the tail > > > alone. It's probably a prioritization issue. Will start looking > > > and update my findings. I can't add devl because of the table but > > > needed to add community that's why ceph-users :-).. Also, wanted > > > to know from Ceph's user if they are also facing similar issues.. > > > > > > > What I meant with lack of parallelism is that at the start of a > > rebuild, there are likely to be many candidate PGs for recovery and > > backfilling, so many things happen at the same time, up to the > > limits of what is configured (max backfill etc). > > > > From looking at my test cluster, it starts with 8-10 backfills and > > recoveries (out of 140 affected PGs), but later on in the game there > > are less and less PGs (and OSDs/nodes) to choose from, so things > > slow down around 60 PGs to just 3-4 backfills. > > And around 20 PGs it's down to 1-2 backfills, so the parallelism is > > clearly gone at that point and recovery speed is down to what a > > single PG/OSD can handle. > > > > Christian > > > > > Thanks & Regards > > > Somnath > > > > > > -----Original Message----- > > > From: Christian Balzer [mailto:ch...@gol.com] > > > Sent: Wednesday, May 11, 2016 12:31 AM > > > To: Somnath Roy > > > Cc: Mark Nelson; Nick Fisk; ceph-users@lists.ceph.com > > > Subject: Re: [ceph-users] Weighted Priority Queue testing > > > > > > > > > > > > Hello, > > > > > > not sure if the Cc: to the users ML was intentional or not, but > > > either way. > > > > > > The issue seen in the tracker: > > > http://tracker.ceph.com/issues/15763 > > > and what you have seen (and I as well) feels a lot like the lack > > > of parallelism towards the end of rebuilds. > > > > > > This becomes even more obvious when backfills and recovery > > > settings are lowered. > > > > > > Regards, > > > > > > Christian > > > -- > > > Christian Balzer Network/Systems Engineer > > > ch...@gol.com Global OnLine Japan/Rakuten Communications > > > http://www.gol.com/ > > > PLEASE NOTE: The information contained in this electronic mail > > > message is intended only for the use of the designated > > > recipient(s) named above. If the reader of this message is not the > > > intended recipient, you are hereby notified that you have received > > > this message in error and that any review, dissemination, > > > distribution, or copying of this message is strictly prohibited. > > > If you have received this communication in error, please notify > > > the sender by telephone or e-mail (as shown above) immediately and > > > destroy any and all copies of this message in your possession > > > (whether hard copies or electronically stored copies). > > > > > > > > > -- > > Christian Balzer Network/Systems Engineer > > ch...@gol.com Global OnLine Japan/Rakuten Communications > > http://www.gol.com/ > > _______________________________________________ > > ceph-users mailing list > > ceph-users@lists.ceph.com > > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com > > -- Christian Balzer Network/Systems Engineer ch...@gol.com Global OnLine Japan/Rakuten Communications http://www.gol.com/ PLEASE NOTE: The information contained in this electronic mail message is intended only for the use of the designated recipient(s) named above. 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