Part I. Monitoring Ceph

Once you have a running cluster, you may begin monitoring your cluster to ensure that your monitor and OSD daemons are running (high-level). Ceph storage cluster clients must connect to a Ceph monitor and receive the latest version of the Ceph cluster map before they can read and write data to the Ceph pools of the storage cluster. So the monitor cluster must have agreement on the state of the cluster before Ceph clients can read and write data.

Ceph OSDs must peer the placement groups on the primary OSD with the copies of the placement groups on secondary OSDs. If faults arise, peering will reflect something other than the active + clean state.