Dear fellow Ceph users, I run a Ceph cluster providing CephFS to a medium-sized Linux server farm. Originally we used the kernel driver (which on the distro we use shows itself to the cluster as a Luminous client) to mount the file system, however at the time of the upgrade to Squid we became aware of the data-corruption bug associated with the use of root squash and subsequently switched to (the Squid version of) ceph-fuse. Furthermore, I took advantage of the switch to bump the OSD require-min-compat-client to Reef and subsequently switch the balancer mode to upmap-read. Weeks passed and I became aware that despite all the attempted tuning, certain work loads which performed fine using the kernel driver perform _extremely_ poorly using ceph-fuse. A decision has therefore been made to relocate the servers which absolutely must have root squash to a different network-storage solution, switch root squash off for all CephFS clients and revert to the kernel driver. Unfortunately while removing client_mds_auth_caps from CephFS required_client_features and switching the balancer mode back to upmap went without any problems, "ceph osd set-require-min-compat-client luminous" fails with Error EPERM: osdmap current utilizes features that require reef; cannot set require_min_compat_client below that to luminous Is there a way of making the osdmap Luminous-compatible again without losing any data stored on the cluster ()? Thank you in advance for your help! -- MS