Ceph is a free software storage platform designed to present object, block, and file storage from a single distributed computer cluster. Ceph’s main goals are to be completely distributed without a single point of failure, scalable to the exabyte level, and freely-available. The data is replicated, making it fault tolerant
Ceph software runs on commodity hardware. The system is designed to be both self-healing and self-managing and strives to reduce both administrator and budget overhead.
Object Storage
Ceph implements distributed object storage. Ceph’s software libraries provide client applications with direct access to the reliable autonomic distributed object store (RADOS) object-based storage system, and also provide a foundation for some of Ceph’s features, including RADOS Block Device (RBD), RADOS Gateway, and the Ceph File System.
The librados software libraries provide access in C, C++, Java, Python and PHP. The RADOS Gateway also exposes the object store as a RESTful interface which can present as both native Amazon S3 and OpenStack Swift APIs.
Block Device
Ceph’s object storage system allows users to mount Ceph as a thinly provisioned block device. When an application writes data to Ceph using a block device, Ceph automatically stripes and replicates the data across the cluster. Ceph’s RADOS Block Device (RBD) also integrates with kernel virtual machines (KVMs).
Ceph RBD interfaces with the same Ceph object storage system that provides the librados interface and the CephFS file system, and it stores block device images as objects.
Since RBD is built on top of librados, RBD inherits librados’s capabilities, including read-only snapshots and revert to snapshot. By striping images across the cluster, Ceph improves read access performance for large block device images.
FileSystem
Ceph’s file system (CephFS) runs on top of the same object storage system that provides object storage and block device interfaces.
The Ceph metadata server cluster provides a service that maps the directories and file names of the file system to objects stored within RADOS clusters.
The metadata server cluster can expand or contract, and it can rebalance the file system dynamically to distribute data evenly among cluster hosts. This ensures high performance and prevents heavy loads on specific hosts within the cluster.
