Next, the OSD that runs the Ceph code introduces latency as it processes the request. It is hard to put an exact figure on this, but it is affected by the speed of the CPU. A faster CPU with a higher frequency will run through the code path faster, reducing latency. Early on in this book, the primary OSD would send the request to the other two OSDs in the replica set. These are both processed in parallel so that there is minimal increase in latency going from 2x to 3x replicas, assuming the backend disks can cope with the load.

There is also an extra network hop between the primary and the replicated OSDs, which introduces latency into each request.