When it comes to data storage and management, Ceph uses the CRUSH algorithm, which is an intelligent data distribution mechanism of Ceph. As we discussed in the last recipe, traditional storage systems use a central metadata/index table to know where the user's data is stored. Ceph, on the other hand, uses the CRUSH algorithm to deterministically compute where the data should be written to or read from. Instead of storing metadata, CRUSH computes metadata on demand, thus removing the need for a centralized server/gateway or broker. It empowers Ceph clients to compute metadata, also known as CRUSH lookup, and communicates with OSDs directly.

For a read/write operation to Ceph clusters, clients first contact a Ceph monitor and retrieve a copy of the cluster map, which is inclusive of five maps, namely the monitor, OSD, MDS, and CRUSH and PG...