5 With ``ceph-deploy``, adding and removing monitors is a simple task. You just
6 add or remove one or more monitors on the command line with one command. Before
7 ``ceph-deploy``, the process of `adding and removing monitors`_ involved
8 numerous manual steps. Using ``ceph-deploy`` imposes a restriction: **you may
9 only install one monitor per host.**
11 .. note:: We do not recommend comingling monitors and OSDs on
14 For high availability, you should run a production Ceph cluster with **AT
15 LEAST** three monitors. Ceph uses the Paxos algorithm, which requires a
16 consensus among the majority of monitors in a quorum. With Paxos, the monitors
17 cannot determine a majority for establishing a quorum with only two monitors. A
18 majority of monitors must be counted as such: 1:1, 2:3, 3:4, 3:5, 4:6, etc.
20 See `Monitor Config Reference`_ for details on configuring monitors.
26 Once you create a cluster and install Ceph packages to the monitor host(s), you
27 may deploy the monitor(s) to the monitor host(s). When using ``ceph-deploy``,
28 the tool enforces a single monitor per host. ::
30 ceph-deploy mon create {host-name [host-name]...}
33 .. note:: Ensure that you add monitors such that they may arrive at a consensus
34 among a majority of monitors, otherwise other steps (like ``ceph-deploy gatherkeys``)
37 .. note:: When adding a monitor on a host that was not in hosts initially defined
38 with the ``ceph-deploy new`` command, a ``public network`` statement needs
39 to be added to the ceph.conf file.
44 If you have a monitor in your cluster that you'd like to remove, you may use
45 the ``destroy`` option. ::
47 ceph-deploy mon destroy {host-name [host-name]...}
50 .. note:: Ensure that if you remove a monitor, the remaining monitors will be
51 able to establish a consensus. If that is not possible, consider adding a
52 monitor before removing the monitor you would like to take offline.
55 .. _adding and removing monitors: ../../operations/add-or-rm-mons
56 .. _Monitor Config Reference: ../../configuration/mon-config-ref