Read Affinity in stretch clusters

Read Affinity reduces cross-zone traffic by keeping the data access within the respective data centers.

For stretched clusters deployed in multi-zone environments, the read affinity topology implementation provides a mechanism to help keep traffic within the data center it originated from. Ceph Object Gateway volumes have the ability to read data from an OSD in proximity to the client, according to OSD locations defined in the CRUSH map and topology labels on nodes.

For example, a stretch cluster contains a Ceph Object Gateway primary OSD and replicated OSDs spread across two data centers A and B. If a GET action is performed on an Object in data center A, the READ operation is performed on the data of the OSDs closest to the client in data center A.