Managing Serviceguard 14th Edition, June 2007

Understanding Serviceguard Software Components
Volume Managers for Data Storage
Chapter 3 119
Veritas Cluster Volume Manager (CVM)
NOTE CVM (and CFS - Cluster File System) are supported on some, but not all,
current releases of HP-UX. Check the latest Release Notes for your
version of Serviceguard for up-to-date information
(http://www.docs.hp.com -> High Availability - >
Serviceguard).
You may choose to configure cluster storage with the Veritas Cluster
Volume Manager (CVM) instead of the Volume Manager (VxVM). The
Base-VxVM provides some basic cluster features when Serviceguard is
installed, but there is no support for software mirroring, dynamic
multipathing (for active/active storage devices), or numerous other
features that require the additional licenses.
VxVM supports up to 16 nodes, and CVM supports up to 8. CFS 5.0 also
supports up to 8 nodes; earlier versions of CFS support up to 4.
The VxVM Full Product and CVM are enhanced versions of the VxVM
volume manager specifically designed for cluster use. When installed
with the Veritas Volume Manager, the CVM add-on product provides
most of the enhanced VxVM features in a clustered environment. CVM is
truly cluster-aware, obtaining information about cluster membership
from Serviceguard directly.
Cluster information is provided via a special system multi-node package,
which runs on all nodes in the cluster. The cluster must be up and must
be running this package before you can configure VxVM disk groups for
use with CVM. Disk groups must be created from the CVM Master node.
The Veritas CVM package for version 3.5 is named VxVM-CVM-pkg; the
package for CVM version 4.1 and later is named SG-CFS-pkg.
CVM allows you to activate storage on one node at a time, or you can
perform write activation on one node and read activation on another
node at the same time (for example, allowing backups). CVM provides
full mirroring and dynamic multipathing (DMP) for clusters.
CVM supports concurrent storage read/write access between multiple
nodes by applications which can manage read/write access contention,
such as Oracle Real Application Cluster (RAC).