Hi guys, recently I took over a care of Ceph cluster that is extremely unbalanced. Cluster is running on Quincy 17.2.7 (upgraded Nautilus -> Octopus -> Quincy) and has 1428 OSDs (HDDs). We are running CephFS on it. Crush failure domain is datacenter (there are 3), data pool is EC 3+3. This cluster had and has balancer disabled for years. And was "balanced" manually by changing OSDs crush weights. So now it is complete mess and I would like to change it to have OSDs crush weight same (3.63898) and to enable balancer with upmap. From `ceph osd df ` sorted from the least used to most used OSDs: ID CLASS WEIGHT REWEIGHT SIZE RAW USE DATA OMAP META AVAIL %USE VAR PGS STATUS MIN/MAX VAR: 0.76/1.16 STDDEV: 5.97 TOTAL 5.1 PiB 3.7 PiB 3.7 PiB 2.9 MiB 8.5 TiB 1.5 PiB 71.50 428 hdd 3.63898 1.00000 3.6 TiB 2.0 TiB 2.0 TiB 1 KiB 5.6 GiB 1.7 TiB 54.55 0.76 96 up 223 hdd 3.63898 1.00000 3.6 TiB 2.0 TiB 2.0 TiB 3 KiB 5.6 GiB 1.7 TiB 54.58 0.76 95 up ... ... ... 591 hdd 3.53999 1.00000 3.6 TiB 3.0 TiB 3.0 TiB 1 KiB 7.0 GiB 680 GiB 81.74 1.14 125 up 832 hdd 3.59999 1.00000 3.6 TiB 3.0 TiB 3.0 TiB 4 KiB 6.9 GiB 680 GiB 81.75 1.14 114 up 248 hdd 3.63898 1.00000 3.6 TiB 3.0 TiB 3.0 TiB 3 KiB 7.2 GiB 646 GiB 82.67 1.16 121 up 559 hdd 3.63799 1.00000 3.6 TiB 3.0 TiB 3.0 TiB 0 B 7.0 GiB 644 GiB 82.70 1.16 123 up TOTAL 5.1 PiB 3.7 PiB 3.6 PiB 2.9 MiB 8.5 TiB 1.5 PiB 71.50 MIN/MAX VAR: 0.76/1.16 STDDEV: 5.97 crush rule: { "rule_id": 10, "rule_name": "ec33hdd_rule", "type": 3, "steps": [ { "op": "set_chooseleaf_tries", "num": 5 }, { "op": "set_choose_tries", "num": 100 }, { "op": "take", "item": -2, "item_name": "default~hdd" }, { "op": "choose_indep", "num": 3, "type": "datacenter" }, { "op": "choose_indep", "num": 2, "type": "osd" }, { "op": "emit" } ] } My question is what would be proper and most safer way to make it happen. * should I first enable balancer and let it do its work and after that change the OSDs crush weights to be even? * or should it otherwise - first to make crush weights even and then enable the balancer? * or is there another safe(r) way? What are the ideal balancer settings for that? I'm expecting a large data movement, and this is production cluster. I'm also afraid that during the balancing or changing crush weights some OSDs become full. I've tried that already and had to move some PGs manually to another OSDs in the same failure domain. I would appreciate any suggestion on that. Thank you!