Usually, a Ceph cluster is deployed with more than one MON instance for increased reliability and availability. Since there are a large number of monitors, they should attain a quorum to make the cluster function properly. Monitoring of MONs regularly is of utmost importance.
To display the cluster MON status and MON map, use the ceph command with either mon stat or mon dump as the suboption:
# ceph mon stat # ceph mon dump
The following figure displays the output of this command:
To maintain a quorum between Ceph MONs, the cluster should always have more than 51 percent of available monitors in a Ceph cluster. Checking the quorum status of a cluster is very useful at the time of MON troubleshooting. You can check the quorum status by using the ceph command and the quorum_status subcommand:
# ceph quorum_status
The quorum status displays election_epoch, which is the election version number, and quorum_leader_name, which denotes the hostname of the quorum leader. It also displays the MON map epoch, cluster ID, and cluster creation date. Each cluster monitor is allocated with a rank. For I/O operations, clients first connect to quorum lead monitors if the leader MON is unavailable; the client then connects to the next rank monitor.