Learning Ceph - Second Edition

CephFS MetaData server (MDS)

In order to manage and provide the hierarchy of data as presented in the context of a familiar tree-organized filesystem, Ceph needs to store additional metadata given the semantics expected:

• Permissions
• Hierarchy
• Names
• Timestamps
• Owners
• Mostly POSIX compliant. mostly.

Unlike legacy systems, the CephFS MDS is designed to facilitate scaling. It is important to note that actual file data does not flow through the Ceph MDS: as with RBD volumes, CephFS clients use the RADOS system to perform bulk data operations directly against a scalable number of distributed OSD storage daemons. In a loose sense, the MDS implements a control plane while RADOS implements the data plane; in fact, the metadata managed by Ceph's ...