.When using the `rolling_update.yml` playbook to upgrade to Red Hat Ceph Storage 3.0 and from version 3.0 to other zStream releases of 3.0, users who use CephFS must manually upgrade the MDS cluster Currently the Metadata Server (MDS) cluster does not have built-in versioning or file system flags to support seamless upgrades of the MDS nodes without potentially causing assertions or other faults due to incompatible messages or other functional differences. For this reason, it's necessary during any cluster upgrade to reduce the number of active MDS nodes for a file system to one, first so that two active MDS nodes do not communicate with different versions. Further, it's also necessary to take standbys offline as any new `CompatSet` flags will propagate via the MDSMap to all MDS nodes and cause older MDS nodes to suicide. To upgrade the MDS cluster: . Reduce the number of ranks to 1: + ---- ceph fs set <fs_name> max_mds 1 ---- . Deactivate all non-zero ranks, from the highest rank to the lowest, while waiting for each MDS to finish stopping: + ---- ceph mds deactivate <fs_name>:<n> ceph status # wait for MDS to finish stopping ---- . Take all standbys offline using `systemctl`: + ---- systemctl stop ceph-mds.target ceph status # confirm only one MDS is online and is active ---- . Upgrade the single active MDS and restart daemon using `systemctl`: + ---- systemctl restart ceph-mds.target ---- . Upgrade and start the standby daemons. . Restore the previous max_mds for your cluster: + ---- ceph fs set <fs_name> max_mds <old_max_mds> ---- For steps on how to upgrade the MDS cluster in a container, refer to the https://access.redhat.com/articles/2789521[Updating Red Hat Ceph Storage deployed as a Container Image] Knowledgebase article.