VERITAS Storage Foundation 4.1 Cluster File System HP Serviceguard Storage Management Suite Extracts, December 2005

CVM Overview
74 Installation and Administration Guide
CVM Overview
The cluster functionality (CVM) of the VERITAS Volume Manager allows multiple hosts
to concurrently access and manage a given set of logical devices under VxVM control. A
VxVM cluster is a set of hosts sharing a set of devices; each host is a node in the cluster.
The nodes are connected across a network. If one node fails, other nodes can still access
the devices. The VxVM cluster feature presents the same logical view of the device
configurations, including changes, on all nodes.
You configure CVM shared storage after setting up a cluster configuration. There must
be at least one non-shared disk on each node for the creation of rootdg to initialize
VxVM. See “CVM Administration” on page 97 for extensive background information on
CVM.
CFS Overview
A file system cluster consists of one primary, and up to fifteen secondaries. The
primary-secondary terminology applies to one file system, not to a specific node (or
hardware platform). So it is possible to have the same cluster node be primary for one
shared file system, while at the same time it is secondary for another shared file system.
Such distribution of file system primaryship to balance the load on a cluster is a
recommended administrative policy (“Distributing the Load on a Cluster” on page 78).
For CVM, a single cluster node is the master for all shared disk groups and shared
volumes in the cluster.
Cluster/Shared Mounts
A VxFS file system that is mounted with the mount –o cluster option is called a cluster
or shared mount, as opposed to a non-shared or local mount. A file system mounted in
shared mode must be on a VxVM shared volume in a cluster environment. A local mount
cannot be remounted in shared mode and a shared mount cannot be remounted in local
mode. File systems in a cluster can be mounted with different read-write options. These
are called asymmetric mounts.