Administrator's Guide

Chapter 4
39
4 Cluster Volume Manager
Administration
A cluster consists of a number of hosts or nodes that share a set of disks. The main
benefits of cluster configurations are:
• Availability—If one node fails, the other nodes can still access the shared disks.
When configured with suitable software, mission-critical applications can continue
running by transferring their execution to a standby node in the cluster. This ability
to provide continuous uninterrupted service by switching to redundant hardware is
commonly termed failover.
Failover is transparent to users and high-level applications for database and
file-sharing. You must configure cluster management software, for example
Serviceguard, to monitor systems and services, and to restart applications on
another node in the event of either hardware or software failure. Serviceguard also
allows you to perform general administrative tasks such as joining or removing
nodes from a cluster.
• Off-host processing—Clusters can reduce contention for system resources by
performing activities such as backup, decision support and report generation on the
more lightly loaded nodes of the cluster. This allows businesses to derive enhanced
value from their investment in cluster systems.
The Cluster Volume Manager (CVM) supports up to 8 nodes in a cluster to
simultaneously access and manage a set of disks under VxVM control (VM disks).
The same logical view of the disk configuration (and any changes to this
configuration) is available on all the nodes. When VxVM cluster functionality is
enabled, all of the nodes in a cluster can share VxVM objects.
This chapter contains the following topics:
• “Overview of Cluster Volume Management” on page 40
• “Private and Shared Disk Groups” on page 41
• “Activation Modes for Shared Disk Groups” on page 42
• “Connectivity Policy of Shared Disk Groups” on page 44
• “Disk Group Failure Policy” on page 45
• “Limitations of Shared Disk Groups” on page 45
• “Recovery in a CVM Environment” on page 46