Tiering modes

There are a number of tiering modes that determine the precise actions of how Ceph reacts to the contents of the HitSets. However, in most cases, the writeback mode will be used. The available modes for use in tiering are writeback, forward, read-forward, proxy, and read-proxy. There are brief descriptions of the available modes and how they act.

Writeback

In writeback mode, data is promoted to the top-level tier by both reads and writes depending on how frequently accessed the object are. Objects in the top-level tier can be modified, and dirty objects will be flushed to the pool at a later date. If an object needs to be read or written to in the bottom tier and the bottom pool supports it, then Ceph will try and directly proxy the operation that has...