We are looking to create a 3 datacenter 4+5 erasure coded pool but can't quite get it to work. Ceph version 17.2.7. These are the hosts (there will eventually be 6 hdd hosts in each datacenter): -33 886.00842 datacenter 714 -7 209.93135 host ceph-hdd1 -69 69.86389 host ceph-flash1 -6 188.09579 host ceph-hdd2 -3 233.57649 host ceph-hdd3 -12 184.54091 host ceph-hdd4 -34 824.47168 datacenter DCN -73 69.86389 host ceph-flash2 -2 201.78067 host ceph-hdd5 -81 288.26501 host ceph-hdd6 -31 264.56207 host ceph-hdd7 -36 1284.48621 datacenter TBA -77 69.86389 host ceph-flash3 -21 190.83224 host ceph-hdd8 -29 199.08838 host ceph-hdd9 -11 193.85382 host ceph-hdd10 -9 237.28154 host ceph-hdd11 -26 187.19536 host ceph-hdd12 -4 206.37102 host ceph-hdd13 We did this: ceph osd erasure-code-profile set DRCMR_k4m5_datacenter_hdd plugin=jerasure k=4 m=5 technique=reed_sol_van crush-root=default crush-failure-domain=datacenter crush-device-class=hdd ceph osd pool create cephfs.hdd.data erasure DRCMR_k4m5_datacenter_hdd ceph osd pool set cephfs.hdd.data allow_ec_overwrites true ceph osd pool set cephfs.hdd.data pg_autoscale_mode warn Didn't quite work: " [WARN] PG_AVAILABILITY: Reduced data availability: 1 pg inactive, 1 pg incomplete pg 33.0 is creating+incomplete, acting [104,219,NONE,NONE,NONE,41,NONE,NONE,NONE] (reducing pool cephfs.hdd.data min_size from 5 may help; search ceph.com/docs for 'incomplete') " I then manually changed the crush rule from this: " rule cephfs.hdd.data { id 7 type erasure step set_chooseleaf_tries 5 step set_choose_tries 100 step take default class hdd step chooseleaf indep 0 type datacenter step emit } " To this: " rule cephfs.hdd.data { id 7 type erasure step set_chooseleaf_tries 5 step set_choose_tries 100 step take default class hdd step choose indep 0 type datacenter step chooseleaf indep 3 type host step emit } " Based on some testing and dialogue I had with Red Hat support last year when we were on RHCS, and it seemed to work. Then: ceph fs add_data_pool cephfs cephfs.hdd.data ceph fs subvolumegroup create hdd --pool_layout cephfs.hdd.data I started copying data to the subvolume and increased pg_num a couple of times: ceph osd pool set cephfs.hdd.data pg_num 256 ceph osd pool set cephfs.hdd.data pg_num 2048 But at some point it failed to activate new PGs eventually leading to this: " [WARN] MDS_SLOW_METADATA_IO: 1 MDSs report slow metadata IOs mds.cephfs.ceph-flash1.agdajf(mds.0): 64 slow metadata IOs are blocked > 30 secs, oldest blocked for 25455 secs [WARN] MDS_TRIM: 1 MDSs behind on trimming mds.cephfs.ceph-flash1.agdajf(mds.0): Behind on trimming (997/128) max_segments: 128, num_segments: 997 [WARN] PG_AVAILABILITY: Reduced data availability: 5 pgs inactive pg 33.6f6 is stuck inactive for 8h, current state activating+remapped, last acting [50,79,116,299,98,219,164,124,421] pg 33.6fa is stuck inactive for 11h, current state activating+undersized+degraded+remapped, last acting [17,408,NONE,196,223,290,73,39,11] pg 33.705 is stuck inactive for 11h, current state activating+undersized+degraded+remapped, last acting [33,273,71,NONE,411,96,28,7,161] pg 33.721 is stuck inactive for 7h, current state activating+remapped, last acting [283,150,209,423,103,325,118,142,87] pg 33.726 is stuck inactive for 11h, current state activating+undersized+degraded+remapped, last acting [234,NONE,416,121,54,141,277,265,19] [WARN] PG_DEGRADED: Degraded data redundancy: 1818/1282640036 objects degraded (0.000%), 3 pgs degraded, 3 pgs undersized pg 33.6fa is stuck undersized for 7h, current state activating+undersized+degraded+remapped, last acting [17,408,NONE,196,223,290,73,39,11] pg 33.705 is stuck undersized for 7h, current state activating+undersized+degraded+remapped, last acting [33,273,71,NONE,411,96,28,7,161] pg 33.726 is stuck undersized for 7h, current state activating+undersized+degraded+remapped, last acting [234,NONE,416,121,54,141,277,265,19] [WARN] POOL_TOO_FEW_PGS: 1 pools have too few placement groups Pool cephfs.hdd.data has 1024 placement groups, should have 2048 [WARN] SLOW_OPS: 3925 slow ops, oldest one blocked for 26012 sec, daemons [osd.17,osd.234,osd.283,osd.33,osd.50] have slow ops. " We had thought it would only affect that particular data pool but eventually everything ground to a halt, also RBD on unrelated replicated pools. Looking at it now I guess that was because the 5 OSDs were blocked for everything and not just the PGs for that data pool? We tried restarting the 5 blocked OSDs to no avail and eventually resorted to deleting the cephfs.hdd.data data pool to restore service. Any suggestions as to what we did wrong? Something to do with min_size? The crush rule? Thanks. Mvh. Torkil -- Torkil Svensgaard Systems Administrator Danish Research Centre for Magnetic Resonance DRCMR, Section 714 Copenhagen University Hospital Amager and Hvidovre Kettegaard Allé 30, 2650 Hvidovre, Denmark