Re: what's the best way to stop an MDS?

Hi all, I am working on a ceph-ansible playbook[1] that removes an MDS from an already deployed Ceph cluster. Going through documentation and ceph-ansible codebase I found out 3 ways to stop an MDS - * ceph fail mds fail <mds-name> && rm -rf /var/lib/cephmds/ceph-{id} [2] * systemctl stop ceph-mds@$HOSTNAME * ceph tell mds.x exit How do these 3 ways compare to each other? I ran these commands on ceph-ansible deployed cluster and all 3 had the very same effect. Is any one of these better than the rest?

What about "ceph mds rm" and "ceph mds rmfailed"? The first time I was

looking for various ways to stop an MDS, I tried "ceph mds fail <mds-name> && ceph mds rm <global-id>" and it did not work since "ceph mds rm" requires an MDS to inactive[3]. Is there a way to render an MDS inactive? I couldn't find one. I also tried "ceph mds fail <mds-name> && ceph mds rmfailed <mds-rank>" but this did not stop MDS. It only changed MDS's state to 'standby" - (teuth-venv) $ ./bin/ceph fs dump | grep -A 1 standby_count_wanted 2> /dev/null dumped fsmap epoch 4 standby_count_wanted 0 4232: [v2:192.168.0.217:6826/2113356090,v1:192.168.0.217:6827/2113356090] 'a' mds.0.3 up:active seq 4 (teuth-venv) $ ./bin/ceph mds fail a 2> /dev/null && ./bin/ceph mds rmfailed --yes-i-really-mean-it 0 2> /dev/null && ./bin/ceph fs dump | grep -A 3 Standby 2> /dev/null dumped fsmap epoch 6 Standby daemons: 4286: [v2:192.168.0.217:6826/401505106,v1:192.168.0.217:6827/401505106] 'a' mds.-1.0 up:standby seq 1 (teuth-venv) $ Also, I find the usage of "remove" in this doc[2] ambiguous -- it can mean removing MDS from cluster by changing MDS's state to standby or it can mean killing/stopping it altogether. Reading [2] my impression was that it meant killing/stopping it but "remove" is also used to describe "ceph mds rm" and "ceph mds rmfailed" commands. Of these, at least "ceph mds rmfailed" does not stop the MDS. If I am not the only one to find this ambiguous, I'll go ahead and change the docs accordingly.

[1] https://github.com/ceph/ceph-ansible/pull/4083 [2] http://docs.ceph.com/docs/master/cephfs/add-remove-mds/ [3] http://docs.ceph.com/docs/master/man/8/ceph/