The Ceph file system (CephFS) is a POSIX-compliant file system that uses a Ceph storage cluster to store its data. CephFS uses the same cluster system as Ceph block devices, Ceph object storage with its S3 and Swift APIs, or native bindings (librados).
To use CephFS, you need to have a running Ceph storage cluster, and at least one running Ceph metadata server.
WARNING: CephFS file layout changes can be performed as documented in http://docs.ceph.com/docs/jewel/cephfs/file-layouts/. However, a data pool must not be added to an existing CephFS file system (via ceph mds add_data_pool) while the file system is mounted by any clients.