[ceph-users] How many MDS servers

Quick question Ceph guru's. For a 1.1PB raw cephfs system currently storing 191TB of data and 390 million objects (mostly small Python, ML training files etc.) how many MDS servers should I be running? System is Nautilus 14.2.8. I ask because up to know I have run one MDS with one standby-replay and occasionally it blows up with large memory consumption, 60Gb+ even though I have mds_cache_memory_limit = 32G and that was 16G until recently. It of course tries to restart on another MDS node fails again and after several attempts usually comes back up. Today I increased to two active MDS's but the question is what is the optimal number for a pretty active system? The single MDS seemed to regularly run around 1400 req/s and I often get up to six clients failing to respond to cache pressure. The current setup is: ceph fs status cephfs - 71 clients ====== +------+----------------+--------+---------------+-------+-------+ | Rank | State | MDS | Activity | dns | inos | +------+----------------+--------+---------------+-------+-------+ | 0 | active | a | Reqs: 447 /s | 12.0M | 11.9M | | 1 | active | b | Reqs: 154 /s | 1749k | 1686k | | 1-s | standby-replay | c | Evts: 136 /s | 1440k | 1423k | | 0-s | standby-replay | d | Evts: 402 /s | 16.8k | 298 | +------+----------------+--------+---------------+-------+-------+ +-----------------+----------+-------+-------+ | Pool | type | used | avail | +-----------------+----------+-------+-------+ | cephfs_metadata | metadata | 160G | 169G | | cephfs_data | data | 574T | 140T | +-----------------+----------+-------+-------+ +-------------+ | Standby MDS | +-------------+ | w | | x | | y | | z | +-------------+ MDS version: ceph version 14.2.8 (2d095e947a02261ce61424021bb43bd3022d35cb) nautilus (stable) Regards. Robert Ruge Systems & Network Manager Faculty of Science, Engineering & Built Environment [cid:image001.png@01D36789.04BE09A0] Important Notice: The contents of this email are intended solely for the named addressee and are confidential; any unauthorised use, reproduction or storage of the contents is expressly prohibited. If you have received this email in error, please delete it and any attachments immediately and advise the sender by return email or telephone. Deakin University does not warrant that this email and any attachments are error or virus free.