[modderation]

Ceph storage uses a hierarchical consistent hashing scheme called "CRUSH" to handle hierarchical data placement and replication across failure domains. Given an object ID, its location can be calculated, and the expected service queried.

As a side effect, it's possible to define a logical topology that reflects the physical layout, spreading data across hosts, racks, or by other arbitrary criteria. Things are exactly where you expect them to be, and there's very little searching involved. Combined with a consistent view of the cluster state, this avoids the need for centralized lookups.

The original paper is a surprisingly short read: https://ceph.com/assets/pdfs/weil-crush-sc06.pdf DOI: 10.1109/SC.2006.19