What is Ceph?
Ceph is a software-defined storage solution designed to address the object, block, and file storage needs of data centres adopting open source as the new norm for high-growth block storage, object stores and data lakes. Ceph provides enterprise scalable storage while keeping CAPEX and OPEX costs in line with underlying bulk commodity disk prices.
What is a Ceph cluster
A Ceph storage cluster consists of the following types of daemons:
- Cluster monitors (
ceph-mon) that maintain the map of the cluster state, keeping track of active and failed cluster nodes, cluster configuration, and information about data placement and manage daemon-client authentications.
- Object storage devices (
ceph-osd) that store data on behalf of Ceph clients. Additionally, they handle data replication, erasure coding, recovery, rebalancing, monitoring and reporting.
- Managers (
ceph-mgr) that maintain cluster runtime metrics, enable dashboarding capabilities and provide an interface to external monitoring systems.
- Metadata servers (
ceph-mds) that store metadata on behalf of the Ceph File System, mapping filenames and directories of the file system to RADOS objects and allow the use of POSIX semantics to access the files.
Ceph stores data as objects within logical storage pools. In order to achieve scalability, rebalancing and recovery capabilities, Ceph shards the pools into placement groups. The CRUSH algorithm then defines the placement group for storing an object and thereafter calculates which Ceph OSD Daemon should store the placement group.