Ceph » CephFS

There is currently no way to gracefully shutdown an active MDS and allow a standby to activate or to transfer the active role to a standby (e.g. using "ceph mds"). The closest existing (documented) command is "ceph mds stop 0" which just returns "'must decrease max_mds or else MDS will immediately reactivate' (-16)".

Without a way to gracefully shutdown the active MDS or transfer away the active role, clients experience a delay after the active MDS goes down, but before a standby is promoted to the active role. This is acceptable in a failure case, but for routine maintenance there needs to be a way to reduce the delay clients experience by proactively transferring the role instead of waiting for failure to be detected.