All the writes will go through the journal. It may happen your SSDs are not preconditioned well and after a lot of writes during recovery IOs are stabilized to lower number. This is quite common for SSDs if that is the case. Thanks & Regards Somnath -----Original Message----- From: J-P Methot [mailto:jpmethot@xxxxxxxxxx] Sent: Wednesday, August 19, 2015 1:03 PM To: Somnath Roy; ceph-users@xxxxxxxx Subject: Re: Bad performances in recovery Hi, Thank you for the quick reply. However, we do have those exact settings for recovery and it still strongly affects client io. I have looked at various ceph logs and osd logs and nothing is out of the ordinary. Here's an idea though, please tell me if I am wrong. We use intel SSDs for journaling and samsung SSDs as proper OSDs. As was explained several times on this mailing list, Samsung SSDs suck in ceph. They have horrible O_dsync speed and die easily, when used as journal. That's why we're using Intel ssds for journaling, so that we didn't end up putting 96 samsung SSDs in the trash. In recovery though, what is the ceph behaviour? What kind of write does it do on the OSD SSDs? Does it write directly to the SSDs or through the journal? Additionally, something else we notice: the ceph cluster is MUCH slower after recovery than before. Clearly there is a bottleneck somewhere and that bottleneck does not get cleared up after the recovery is done. On 2015-08-19 3:32 PM, Somnath Roy wrote: > If you are concerned about *client io performance* during recovery, use these settings.. > > osd recovery max active = 1 > osd max backfills = 1 > osd recovery threads = 1 > osd recovery op priority = 1 > > If you are concerned about *recovery performance*, you may want to bump this up, but I doubt it will help much from default settings.. > > Thanks & Regards > Somnath > > -----Original Message----- > From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf > Of J-P Methot > Sent: Wednesday, August 19, 2015 12:17 PM > To: ceph-users@xxxxxxxx > Subject: Bad performances in recovery > > Hi, > > Our setup is currently comprised of 5 OSD nodes with 12 OSD each, for a total of 60 OSDs. All of these are SSDs with 4 SSD journals on each. The ceph version is hammer v0.94.1 . There is a performance overhead because we're using SSDs (I've heard it gets better in infernalis, but we're not upgrading just yet) but we can reach numbers that I would consider "alright". > > Now, the issue is, when the cluster goes into recovery it's very fast at first, but then slows down to ridiculous levels as it moves forward. You can go from 7% to 2% to recover in ten minutes, but it may take 2 hours to recover the last 2%. While this happens, the attached openstack setup becomes incredibly slow, even though there is only a small fraction of objects still recovering (less than 1%). The settings that may affect recovery speed are very low, as they are by default, yet they still affect client io speed way more than it should. > > Why would ceph recovery become so slow as it progress and affect client io even though it's recovering at a snail's pace? And by a snail's pace, I mean a few kb/second on 10gbps uplinks. > -- > ====================== > Jean-Philippe Méthot > Administrateur système / System administrator GloboTech Communications > Phone: 1-514-907-0050 > Toll Free: 1-(888)-GTCOMM1 > Fax: 1-(514)-907-0750 > jpmethot@xxxxxxxxxx > http://www.gtcomm.net > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.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). > -- ====================== Jean-Philippe Méthot Administrateur système / System administrator GloboTech Communications Phone: 1-514-907-0050 Toll Free: 1-(888)-GTCOMM1 Fax: 1-(514)-907-0750 jpmethot@xxxxxxxxxx http://www.gtcomm.net _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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