When managing shared storage on a cluster, every node must be informed about changes that are done to the storage subsystem. The Linux Volume Manager 2 (LVM2), which is widely used to manage local storage, has been extended to support transparent management of volume groups across the whole cluster. Clustered volume groups can be managed using the same commands as local storage.
To implement cLVM, a shared storage setup — such as provided by a Fire Channel, FCoE, SCSI or iSCSI SAN or DRBD — must be available.
Internally, cLVM uses the Distributed Lock Manager (DLM) component of the cluster stack to coordinate access to the LVM2 metadata. As DLM in turn integrates with the other components of the stack such as fencing, the integrity of the shared storage is protected at all times.
cLVM does not coordinate access to the shared data itself; to do so, you must configure OCFS2 or other cluster-aware applications on top of the cLVM-managed storage.