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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
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