Cluster maps

The cluster map is a composite of maps, including the monitor map, the OSD map, and the placement group map. The cluster map tracks a number of important events:

• Which processes are in the IBM Storage Ceph cluster.

• Which processes that are in the IBM Storage Ceph cluster are up and running or down.

• Whether, the placement groups are active or inactive, and clean or in some other state.

• Other details that reflect the current state of the cluster, such as:

  • the total amount of storage space or

  • the amount of storage used.

When there is a significant change in the state of the cluster, for example, a Ceph OSD goes down, a placement group falls into a degraded state, and so on. The cluster map gets updated to reflect the current state of the cluster. Additionally, the Ceph monitor also maintains a history of the prior states of the cluster. The monitor map, OSD map, and placement group map each maintain a history of their map versions. Each version is called an epoch.

When operating the IBM Storage Ceph cluster, keeping track of these states is an important part of the cluster administration.