Let's have a quick recap of how clients access the Ceph cluster. To perform a write operation with the Ceph cluster, the client gets the latest copy of the cluster map from the Ceph monitor (if they do not have it already). The cluster map provides information about the Ceph cluster layout. Then the client writes/reads the object, which is stored on a Ceph pool. The pool selects OSDs based on the CRUSH ruleset for that pool. The following diagram illustrates this entire process:

Now, let's understand the process of data storage inside the Ceph cluster. Ceph stores data in logical partitions known as pools. These pools hold multiple PGs, which in turn hold objects. Ceph is a true distributed storage system in which each object is replicated and stored across different OSDs each time. This mechanism has been explained with the help of the following diagram, in which I have tried to present how objects get stored in the Ceph cluster: