Based on the book 'Learning Ceph' (https://www.packtpub.com/application-development/learning-ceph), chapter performance tuning, we swapped the values for osd_recovery_op_priority and osd_client_op_priority to 60 and 40. "... osd recovery op priority: This is the priority set for recovery operation. Lower the number, higher the recovery priority. Higher recovery priority might cause performance degradation until recovery completes. " So when setting the value for recovery_op_priority higher then the value for client_op_priority the client requests should have higher priority than recovery requests. Since setting the parameters to these values (Giant 0.87.2) our client performance is fine when OSD's are removed or added to the cluster (e.g adding 25 osd's to the cluster, having 20 OSD's until then). Increasing osd_max_backfills higher than 2 again reduces the effect. Maybe this helps. Regards Steffen >>> Robert LeBlanc <robert@xxxxxxxxxxxxx> 10.09.2015 22:56 >>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 We are trying to add some additional OSDs to our cluster, but the impact of the backfilling has been very disruptive to client I/O and we have been trying to figure out how to reduce the impact. We have seen some client I/O blocked for more than 60 seconds. There has been CPU and RAM head room on the OSD nodes, network has been fine, disks have been busy, but not terrible. 11 OSD servers: 10 4TB disks with two Intel S3500 SSDs for journals (10GB), dual 40Gb Ethernet, 64 GB RAM, single CPU E5-2640 Quanta S51G-1UL. Clients are QEMU VMs. [ulhglive-root@ceph5 current]# ceph --version ceph version 0.94.2 (5fb85614ca8f354284c713a2f9c610860720bbf3) Some nodes are 0.94.3 [ulhglive-root@ceph5 current]# ceph status cluster 48de182b-5488-42bb-a6d2-62e8e47b435c health HEALTH_WARN 3 pgs backfill 1 pgs backfilling 4 pgs stuck unclean recovery 2382/33044847 objects degraded (0.007%) recovery 50872/33044847 objects misplaced (0.154%) noscrub,nodeep-scrub flag(s) set monmap e2: 3 mons at {mon1=10.217.72.27:6789/0,mon2=10.217.72.28:6789/0,mon3=10.217.72.29:6789/0} election epoch 180, quorum 0,1,2 mon1,mon2,mon3 osdmap e54560: 125 osds: 124 up, 124 in; 4 remapped pgs flags noscrub,nodeep-scrub pgmap v10274197: 2304 pgs, 3 pools, 32903 GB data, 8059 kobjects 128 TB used, 322 TB / 450 TB avail 2382/33044847 objects degraded (0.007%) 50872/33044847 objects misplaced (0.154%) 2300 active+clean 3 active+remapped+wait_backfill 1 active+remapped+backfilling recovery io 70401 kB/s, 16 objects/s client io 93080 kB/s rd, 46812 kB/s wr, 4927 op/s Each pool is size 4 with min_size 2. One problem we have is that the requirements of the cluster changed after setting up our pools, so our PGs are really out of wack. Our most active pool has only 256 PGs and each PG is about 120 GB is size. We are trying to clear out a pool that has way too many PGs so that we can split the PGs in that pool. I think these large PGs is part of our issues. Things I've tried: * Lowered nr_requests on the spindles from 1000 to 100. This reduced the max latency sometimes up to 3000 ms down to a max of 500-700 ms. it has also reduced the huge swings in latency, but has also reduced throughput somewhat. * Changed the scheduler from deadline to CFQ. I'm not sure if the the OSD process gives the recovery threads a different disk priority or if changing the scheduler without restarting the OSD allows the OSD to use disk priorities. * Reduced the number of osd_max_backfills from 2 to 1. * Tried setting noin to give the new OSDs time to get the PG map and peer before starting the backfill. This caused more problems than solved as we had blocked I/O (over 200 seconds) until we set the new OSDs to in. Even adding one OSD disk into the cluster is causing these slow I/O messages. We still have 5 more disks to add from this server and four more servers to add. In addition to trying to minimize these impacts, would it be better to split the PGs then add the rest of the servers, or add the servers then do the PG split. I'm thinking splitting first would be better, but I'd like to get other opinions. No spindle stays at high utilization for long and the await drops below 20 ms usually within 10 seconds so I/O should be serviced "pretty quick". My next guess is that the journals are getting full and blocking while waiting for flushes, but I'm not exactly sure how to identify that. We are using the defaults for the journal except for size (10G). We'd like to have journals large to handle bursts, but if they are getting filled with backfill traffic, it may be counter productive. Can/does backfill/recovery bypass the journal? Thanks, - ---------------- Robert LeBlanc PGP Fingerprint 79A2 9CA4 6CC4 45DD A904 C70E E654 3BB2 FA62 B9F1 -----BEGIN PGP SIGNATURE----- Version: Mailvelope v1.0.2 Comment: https://www.mailvelope.com wsFcBAEBCAAQBQJV8e5qCRDmVDuy+mK58QAAaIwQAMN5DJlhrZkqwqsVXaKB nnegQjG6Y02ObLRrg96ghHr+AGgY/HRm3iShng6E1N9CL+XjcHSLeb1JqH9n 2SgGQGoRAU1dY6DIlOs5K8Fwd2bBECh863VymYbO+OLgtXbpp2mWfZZVAkTf V9ryaEh7tZOY1Mhx7mSIyr9Ur7IxTUOjzExAFPGfTLP1cbjE/FXoQMHh10fe zSzk/qK0AvajFD0PR04uRyEsGYeCLl68kGQi1R7IQlxZWc7hMhWXKNIFlbKB lk5+8OGx/LawW7qxpFm8a1SNoiAwMtrPKepvHYGi8u3rfXJa6ZE38jGuoqRs 8jD+b+gS0yxKbahT6S/gAEbgzAH0JF4YSz+nHNrvS6eSebykE9/7HGe9W7WA HRAkrESi/f1MKtRkud2Nhycx2R0MZLK/HoumnCN8WUmgvOtKsyYpXj6FXghv VGpi3r6uyC5Xlb8JGREqB1hAUTHAv0+z4biDBvPYrENwFUaerWiIujIeLWV9 aYuiQBjjDCLoqWZj0+gQwn9/zXo8gE7jo3XAemYqGB8NJY1e+RZW6+TgC2rD Floa1en1PzZsynm1Ho+RPWW509kog5fFkt41nJmmxRi3kNWwiJfKLJvysetl RYudFG1cEumfI68VyNcuL4dMzf9FsiADsBaHue8g9a5bjJH8LjK4fKZDCCJf Rzgu =vlrz -----END PGP SIGNATURE----- _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com -- Klinik-Service Neubrandenburg GmbH Allendestr. 30, 17036 Neubrandenburg Amtsgericht Neubrandenburg, HRB 2457 Geschaeftsfuehrerin: Gudrun Kappich _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
 |