ceph-performancelisted

# ceph-performance Defaults read from `src/common/options/*.yaml.in` at v19.2.6 and v20.2.4, docs.ceph.com (tentacle pages) and Rook docs at v1.20.7, on **2026-09-23**. Measure before and after every change; `ceph config show osd.N <opt>` is the value actually in force. ## mClock: the NVMe capacity trap mClock sizes every reservation from each OSD's measured IOPS capacity. At OSD start an `osd bench` sets `osd_mclock_max_capacity_iops_{hdd,ssd}`. If the result exceeds the sanity threshold — **500 (HDD), 80 000 (SSD)** — it is discarded and the OSD falls back to the default capacity (**21 500** SSD) with a cluster-log warning. Modern NVMe routinely exceeds 80 000, so mClock under-drives it. 1. `ceph config show osd.N osd_mclock_max_capacity_iops_ssd` on every OSD; `21500` means the fallback hit. 2. Measure the device with fio at 4 KiB random write, then `ceph config set osd.N osd_mclock_max_capacity_iops_ssd <iops>`. 3. Re-check after replacing a device — the value is per OSD. Profiles: `balanced` is the default from 17.2.7 and in Reef, Squid and Tentacle (17.2.0–17.2.6 shipped `high_client_ops`). Use `high_client_ops` for latency-sensitive steady state, `high_recovery_ops` only for a maintenance window. ## Memory - Under Rook, Ceph reads `POD_MEMORY_REQUEST` and uses it 1:1 as `osd_memory_target`; with only a limit, target = limit × `osd_memory_target_cgroup_limit_ratio` (0.8). Set requests and limits explicitly on `spec.resources.osd`; the limit needs head