[ceph-users] Poor performance after (incomplete?) upgrade to Nautilus

Hi all, since a few weeks our Nautilus cluster was struggling with severe performance issues. When an OSD would go down, the rebalancing was really slow. Long periods with no data transfer at all (client and rebalancing!) and times with rebalancing traffic only. However, client traffic was almost stalled for the whole period until all objects were in place again (VMs were frozen). PGs were stuck in peering or inactive for long times. Sometimes we had to restart the ceph-mon in order to get the whole process running again. The issues started all of a sudden, we don't remember doing any changes to the configuration. The whole cluster has been updated from Mimic to Nautilus (14.2.3) in September while the issue occurred just a few weeks ago. Updating it to 14.2.5 did not resolve the issue back then. Looking through mailing lists I found the following message: http://lists.ceph.com/pipermail/ceph-users-ceph.com/2018-July/028035.html So I ran "ceph osd require-osd-release nautilus" and all of a sudden the problems where gone! I do not recall executing that command right after the upgrade because the documentation states "Complete the upgrade by disallowing pre-Nautilus OSDs and enabling all new Nautilus-only functionality.". As by that point in time all OSDs, MONs and MGRs were successfully updated there was no reason to believe this command would be necessary. Therefore I got two questions: 1. What exactly does the command do besides preventing old OSDs from joining? 2. What could have been the issue with the cluster and how did this command fix it? If it is really that important to run the command, the docs should state this more clearly. I appreciate any insight on this topic. Thanks, Georg