Hi Alexander, that sounds pretty promising to me. I've checked bluestore_min_alloc_size and most 1370 OSDs have value 65536. You mentioned: "You will have to do that weekly until you redeploy all OSDs that were created with 64K bluestore_min_alloc_size" Is it the only way to approach this, that each OSD has to be recreated? Thank you for reply dp On 3/24/24 12:44 PM, Alexander E. Patrakov wrote:
Hi Denis,
My approach would be:
1. Run "ceph osd metadata" and see if you have a mix of 64K and 4K bluestore_min_alloc_size. If so, you cannot really use the built-in balancer, as it would result in a bimodal distribution instead of a proper balance, see https://tracker.ceph.com/issues/64715, but let's ignore this little issue if you have enough free space. 2. Change the weights as appropriate. Make absolutely sure that there are no reweights other than 1.0. Delete all dead or destroyed OSDs from the CRUSH map by purging them. Ignore any PG_BACKFILL_FULL warnings that appear, they will be gone during the next step. 3. Run this little script from Cern to stop the data movement that was just initiated: https://raw.githubusercontent.com/cernceph/ceph-scripts/master/tools/upmap/u..., pipe its output to bash. This should cancel most of the data movement, but not all - the script cannot stop the situation when two OSDs want to exchange their erasure-coded shards, like this: [1,2,3,4] -> [1,3,2,4]. 4. Set the "target max misplaced ratio" option for MGR to what you think is appropriate. The default is 0.05, and this means that the balancer will enable at most 5% of the PGs to participate in the data movement. I suggest starting with 0.01 and increasing if there is no visible impact of the balancing on the client traffic. 5. Enable the balancer.
If you think that https://tracker.ceph.com/issues/64715 is a problem that would prevent you from using the built-in balancer:
4. Download this script: https://raw.githubusercontent.com/TheJJ/ceph-balancer/master/placementoptimi... 5. Run it as follows: ./placementoptimizer.py -v balance --osdsize device --osdused delta --max-pg-moves 500 --osdfrom fullest | bash
This will move at most 500 PGs to better places, starting with the fullest OSDs. All weights are ignored, and the switches take care of the bluestore_min_alloc_size overhead mismatch. You will have to do that weekly until you redeploy all OSDs that were created with 64K bluestore_min_alloc_size.
A hybrid approach (initial round of balancing with TheJJ, then switch to the built-in balancer) may also be viable.
On Sun, Mar 24, 2024 at 7:09 PM Denis Polom <denispolom@gmail.com> wrote:
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.
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