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