quincy 17.2.6 - write performance continuously slowing down until OSD restart needed

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Hello dear CEPH users and developers,

we're dealing with strange problems.. we're having 12 node alma linux 9 cluster,
initially installed CEPH 15.2.16, then upgraded to 17.2.5. It's running bunch
of KVM virtual machines accessing volumes using RBD.

everything is working well, but there is strange and for us quite serious issue
 - speed of write operations (both sequential and random) is constantly degrading
 drastically to almost unusable numbers (in ~1week it drops from ~70k 4k writes/s
 from 1 VM  to ~7k writes/s)

When I restart all OSD daemons, numbers immediately return to normal..

volumes are stored on replicated pool of 4 replicas, on top of 7*12 = 84
INTEL SSDPE2KX080T8 NVMEs.

I've updated cluster to 17.2.6 some time ago, but the problem persists. This is
especially annoying in connection with https://tracker.ceph.com/issues/56896
as restarting OSDs is quite painfull when half of them crash..

I don't see anything suspicious, nodes load is quite low, no logs errors,
network latency and throughput is OK too

Anyone having simimar issue?

I'd like to ask for hints on what should I check further..

we're running lots of 14.2.x and 15.2.x clusters, none showing similar
issue, so I'm suspecting this is something related to quincy

thanks a lot in advance

with best regards

nikola ciprich



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Ing. Nikola CIPRICH
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