ceph架构简单流程

Ceph clients use the following steps to compute PG IDs.

1. The client inputs the pool ID and the object ID. (e.g., pool = "liverpool" and object-id = "john")
2. CRUSH takes the object ID and hashes it.
3. CRUSH calculates the hash modulo of the number of PGs. (e.g., 58) to get a PG ID.
4. CRUSH calculates the primary OSD corresponding to the PG ID.
5. The client gets the pool ID given the pool name (e.g., "liverpool" = 4)
6. The client prepends the pool ID to the PG ID (e.g., 4.58).
7. The client performs an object operation (e.g., write, read, delete, etc.) by communicating directly with the Primary OSD in the Acting Set.

参考:https://access.redhat.com/documentation/en/red-hat-ceph-storage/1.3/architecture-guide/chapter-2-storage-cluster-architecture