Hi all, There's something broken in our env when we try to add new mons to existing clusters, confirmed on two clusters running mimic and nautilus. It's basically this issue https://tracker.ceph.com/issues/42830 In case something is wrong with our puppet manifests, I'm trying to doing it manually. First we --mkfs the mon and start it, but as soon as the new mon starts synchronizing, the existing leader becomes unresponsive and an election is triggered. Here's exactly what I'm doing: # cd /var/lib/ceph/tmp/ # scp cephmon1:/var/lib/ceph/tmp/keyring.mon.cephmon1 keyring.mon.cephmon4 # ceph mon getmap -o monmap # ceph-mon --mkfs -i cephmon4 --monmap monmap --keyrin keyring.mon.cephmon4 --setuser ceph --setgroup ceph # vi /etc/ceph/ceph.conf <add the new mon to ceph.conf like this> [mon.cephmon4] host = cephmon4 mon addr = a.b.c.d:6790 # systemctl start ceph-mon@cephmon4 The log file on the new mon shows it start synchronizing, then immediately the CPU usage on the leader goes to 100% and elections start happening, and ceph health shows mon slow ops. perf top of the ceph-mon with 100% CPU is shown below [1]. On a small nautilus cluster, the new mon gets added withing a minute or so (but not cleanly -- the leader is unresponsive for quite awhile until the new mon joins). debug_mon=20 on the leader doesn't show anything very interesting. On our large mimic cluster we tried waiting more than 10 minutes -- suffering through several mon elections and 100% usage bouncing around between leaders -- until we gave up. I'm pulling my hair out a bit on this -- it's really weird! Did anyone add a new mon to an existing large cluster recently, and it went smoothly? Cheers, Dan [1] 15.12% ceph-mon [.] MonitorDBStore::Transaction::encode 8.95% libceph-common.so.0 [.] ceph::buffer::v14_2_0::ptr::append 8.68% libceph-common.so.0 [.] ceph::buffer::v14_2_0::list::append 7.69% libceph-common.so.0 [.] ceph::buffer::v14_2_0::ptr::release 5.86% libceph-common.so.0 [.] ceph::buffer::v14_2_0::ptr::ptr