yum install python-rados
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A Ceph Client, via librados, interacts directly with OSDs to store and retrieve data. To interact with OSDs, the client app must invoke librados and connect to a Ceph Monitor. Once connected, librados retrieves the Cluster Map from the Ceph Monitor. When the client app wants to read or write data, it creates an I/O context and binds to a pool. The pool has an associated CRUSH Rule that defines how it will place data in the storage cluster. Via the I/O context, the client provides the object name to librados, which takes the object name and the cluster map (i.e., the topology of the cluster) and computes the placement group and OSD for locating the data. Then the client application can read or write data. The client app doesn’t need to learn about the topology of the cluster directly.