Ceph can run with a cluster containing thousands of Object Storage Devices (OSDs). A minimal system will have at least two OSDs for data replication. To configure OSD clusters, you must provide settings in the configuration file. Ceph provides default values for many settings, which you can override in the configuration file. Additionally, you can make runtime modification to the configuration using command-line utilities.

When Ceph starts, it activates three daemons:

  • ceph-mon (mandatory)
  • ceph-osd (mandatory)
  • ceph-mds (mandatory for cephfs only)

Each process, daemon or utility loads the host’s configuration file. A process may have information about more than one daemon instance (i.e., multiple contexts). A daemon or utility only has information about a single daemon instance (a single context).


Ceph can run on a single host for evaluation purposes.

Configuring the Object Store

For general object store configuration, refer to the following:


To optimize the performance of your cluster, refer to the following: