Hi Niklas, Most admins who haven't taken the time to tame this somewhat wild animal, like myself, will tell you to disable it and choose for yourself the amount of PGs that you think is right to allocate to each pool to get as many OSDs as possible to participate by distributing the budget of 150-200 PGs/ HDD OSD among all the pools in the best way possible.
But you could try setting the autoscaler to "warn" mode and modifying the target_size_ratio and/or setting the bulk flag on the "large" pools (those containing the most data or the most objects) to see what it will do and then decide whether to apply its recommendations if they seem relevant to you. These two blog posts [1] [2] should shed some light on the subject. Regards, Frédéric. [1] https://ceph.io/en/news/blog/2019/new-in-nautilus-pg-merging-and-autotuning/ [2] https://ceph.io/en/news/blog/2022/autoscaler_tuning/ ________________________________ De : Niklas Hambüchen <m...@nh2.me> Envoyé : samedi 21 juin 2025 02:22 À : ceph-users@ceph.io Objet : [ceph-users] Suspiciously low PG count for CephFS with many small files I have 2 clusters; both have HDDs and SSDs. Reporting only the HDDs which have their own pools: "rep-cluster": hdd-pool 3-replication, 86 OSDs (16 TiB each), 1024 PGs, 78 %RAW USED, 100 M objects "ec-cluster": hdd-pool erasure k=4 m=2, 58 OSDs (16 TiB each), 256 PGs, 60 %RAW USED, 450 M objects Both are Ceph 18.2.1, Bluestore, and have the autoscaler enabled. As you can see, I have many small objects. My PGs-copies-per-OSD seem far off from the recommendation of 100 PGs per OSD (`mon_target_pg_per_osd`): rep-cluster: 35 PGs/OSD (= 1024*3/86) ec-cluster: 26 PGs/OSD (= 256*6/58) So I'm at least 3x-4x off. Why? Should the autoscaler not have increased the PGs here? `ceph osd pool autoscale-status`: rep-cluster: POOL SIZE TARGET SIZE RATE RAW CAPACITY RATIO TARGET RATIO EFFECTIVE RATIO BIAS PG_NUM NEW PG_NUM AUTOSCALE BULK data 349.4T 3.0 1343T 0.7802 1.0 1024 on False ec-cluster: data_ec 347.3T 1.5 876.4T 0.5944 1.0 256 on False I believe that because of this I suffer some drawbacks: * On ec-cluster, a PG contains ~2 TiB and ~2 M objects, causing rebalances to happen in coarse, slow steps. Should I take some steps to force the autoscaler to increase PGs, and if yes, which approach would be best here? Thanks for your tips! Niklas _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-le...@ceph.io
