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Summary

In this chapter, you learned:

  • The CRUSH algorithm provides a decentralized way for Ceph clients to interact with the Red Hat Ceph Storage cluster, which enables massive scalability.

  • The CRUSH map contains two main components: a hierarchy of buckets that organize OSDs into a treelike structure where the OSDs are the leaves of the tree, and at least one CRUSH rule that determines how Ceph assigns PGs to OSDs from the CRUSH tree.

  • Ceph provides various command-line tools to display, tune, modify, and use the CRUSH map.

  • You can modify the CRUSH algorithm's behavior by using tunables, which disable, enable, or adjust features of the CRUSH algorithm.

  • The OSD map epoch is the map's revision number and increments whenever a change occurs. Ceph updates the OSD map every time an OSD joins or leaves the cluster and OSDs keep the map synchronized among themselves.

Revision: cl260-5.0-29d2128