Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

Campus cluster configurations (also known as stretch cluster or remote mirror
configurations) can also be configured and administered.
See “About sites and remote mirrors” on page 487.
Overview of cluster volume management
In recent years, tightly-coupled cluster systems have become increasingly popular
in the realm of enterprise-scale mission-critical data processing. The primary
advantage of clusters is protection against hardware failure. Should the primary
node fail or otherwise become unavailable, applications can continue to run by
transferring their execution to standby nodes in the cluster. This ability to provide
continuous availability of service by switching to redundant hardware is commonly
termed failover.
Another major advantage of clustered systems is their ability to reduce contention
for system resources caused by activities such as backup, decision support and
report generation. Businesses can derive enhanced value from their investment
in cluster systems by performing such operations on lightly loaded nodes in the
cluster rather than on the heavily loaded nodes that answer requests for service.
This ability to perform some operations on the lightly loaded nodes is commonly
termed load balancing.
The cluster functionality of VxVM works together with the cluster monitor daemon
that is provided by VCS or by the host operating system. The cluster monitor
informs VxVM of changes in cluster membership. Each node starts up
independently and has its own cluster monitor plus its own copies of the operating
system and VxVM with support for cluster functionality. When a node joins a
cluster, it gains access to shared disk groups and volumes. When a node leaves a
cluster, it no longer has access to these shared objects. A node joins a cluster when
you issue the appropriate command on that node.
In an HP Serviceguard cluster, a node can join the cluster automatically at boot
time.
Warning: The cluster functionality of VxVM is supported only when used in
conjunction with a cluster monitor that has been configured correctly to work
with VxVM.
Figure 13-1 shows a simple cluster arrangement consisting of four nodes with
similar or identical hardware characteristics (CPUs, RAM and host adapters), and
configured with identical software (including the operating system).
453Administering cluster functionality
Overview of cluster volume management