Dear Cephalopodians, as part of our stress test with 100,000,000 objects (all small files) we ended up with the following usage on the OSDs on which the metadata pool lives: # ceph osd df | head ID CLASS WEIGHT REWEIGHT SIZE USE AVAIL %USE VAR PGS [...] 2 ssd 0.21819 1.00000 223G 79649M 145G 34.81 6.62 128 3 ssd 0.21819 1.00000 223G 79697M 145G 34.83 6.63 128
The cephfs-data cluster is mostly empty (5 % usage), but contains 100,000,000
small objects.
Looking with:
ceph daemon osd.2 perf dump
I get:
"bluefs": {
"gift_bytes": 0,
"reclaim_bytes": 0,
"db_total_bytes": 84760592384,
"db_used_bytes": 78920024064,
"wal_total_bytes": 0,
"wal_used_bytes": 0,
"slow_total_bytes": 0,
"slow_used_bytes": 0,
so it seems this is almost exclusively RocksDB usage.
Is this expected?
Is there a recommendation on how much MDS storage is needed for a CephFS with
450 TB?
Cheers,
Oliver
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