Open Source Object Storage for Unstructured Data: Ceph on HP ProLiant SL4540 Gen8 Servers

Reference Architecture| Ceph on HP ProLiant SL4540 Gen8 Servers
Figure 1: Cluster Access Methods
The core of mapping a HTTP GET/PUT or block read/write to Ceph objects from any of the access methods is CRUSH
(Controlled Replication Under Scalable Hashing). It is the algorithm Ceph uses to compute object storage locations. Per the
picture above, all access methods are converted into some number of Ceph native objects on the back end.
The Ceph storage system supports the notion of ‘Pools’, which are logical partitions for storing objects. Pools set the
following parameters:
• Ownership/access of objects
• The number of object replicas
• The number of placement groups
• The CRUSH Rule set to use
Ceph Clients retrieve a cluster map from a Ceph Monitor, and write objects to pools. The pool’s size, number of replicas, the
CRUSH rule set, and the number of placement groups determine how Ceph will place the data.
Figure 2: Client IO to a Pool
Each pool has a number of placement groups (PGs). CRUSH maps PGs to OSDs dynamically. When a Ceph Client stores
objects, CRUSH will map each object to a placement group.
Mapping objects to placement groups creates a layer of indirection between the Ceph OSD Daemon and the Ceph Client. The
Ceph Storage Cluster must be able to grow (or shrink) and rebalance where it stores objects dynamically. If the Ceph Client
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