Chapter 1. Overview

Red Hat Ceph is a distributed data object store designed to provide excellent performance, reliability and scalability. Distributed object stores are the future of storage, because they accommodate unstructured data, and because clients can use modern object interfaces and legacy interfaces simultaneously. For example:

The power of Red Hat Ceph can transform your organization’s IT infrastructure and your ability to manage vast amounts of data, especially for cloud computing platforms like RHEL OSP. Red Hat Ceph delivers extraordinary scalability–thousands of clients accessing petabytes to exabytes of data and beyond.

At the heart of every Ceph deployment is the 'Ceph Storage Cluster.' It consists of two types of daemons:

Ceph client interfaces read data from and write data to the Ceph storage cluster. Clients need the following data to communicate with the Ceph storage cluster:

Ceph clients maintain object IDs and the pool name(s) where they store the objects, but they do not need to maintain an object-to-OSD index or communicate with a centralized object index to look up data object locations. To store and retrieve data, Ceph clients access a Ceph monitor and retrieve the latest copy of the storage cluster map. Then, Ceph clients can provide an object name and pool name, and Ceph will use the cluster map and the CRUSH (Controlled Replication Under Scalable Hashing) algorithm to compute the object placement group and the primary Ceph OSD for storing or retrieving data. The Ceph client connects to the primary OSD where it may perform read and write operations. There is no intermediary server, broker or bus between the client and the OSD.

When an OSD stores data, it receives data from a Ceph client—​whether the client is a Ceph Block Device, a Ceph Object Gateway or another interface—​and it stores the data as an object. Each object corresponds to a file in a filesystem, which is stored on a storage device such as a hard disk. Ceph OSDs handle the read/write operations on the storage device.

Ceph OSDs store all data as objects in a flat namespace (e.g., no hierarchy of directories). An object has a cluster-wide unique identifier, binary data, and metadata consisting of a set of name/value pairs. The semantics are completely up to Ceph clients. For example, the Ceph block device maps a block device image to a series of objects stored across the cluster.