Hi Rich,
I've noticed this a couple of times on Nautilus after doing some large backfill operations. It seems the osd map doesn't clear properly after the cluster returns to Health OK and builds up on the mons. I do a "du" on the mon folder e.g. du -shx /var/lib/ceph/mon/ and this shows several GB of data.
It does, almost 8 GB for <300 OSDs, which increased several-fold over the last weeks (since we started upgrading Nautilus->Pacific). However, I didn't think much of it after reading in the docs about the hardware recommendations that require at least 60 GB per ceph-mon [1].
I give all my mgrs and mons a restart and after a few minutes I can see this osd map data getting purged from the mons. After a while it should be back to a few hundred MB (depending on cluster size). This may not be the problem in your case, but an easy thing to try. Note, if your cluster is being held in Warning or Error by something this can also explain the osd maps not clearing. Make sure you get the cluster back to health OK first.
Thanks for the suggestion, will try that once we reach HEALTH_OK. Best regards, Jan-Philipp [1]: https://docs.ceph.com/en/latest/start/hardware-recommendations/#minimum-hard...