Managing Serviceguard 14th Edition, June 2007

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 67
Figure 3-2 Lock Disk or Lock LUN Operation
Serviceguard periodically checks the health of the lock disk or LUN and
writes messages to the syslog file if the device fails the health check.
This file should be monitored for early detection of lock disk problems.
If you are using a lock disk, you can choose between two lock disk
options—a single or dual lock disk—based on the kind of high
availability configuration you are building. A single lock disk is
recommended where possible. With both single and dual locks, however,
it is important that the cluster lock be available even if the power circuit
to one node fails; thus, the choice of a lock configuration depends partly
on the number of power circuits available. Regardless of your choice, all
nodes in the cluster must have access to the cluster lock to maintain high
availability.
IMPORTANT A dual lock cannot be implemented on LUNs. This means that the Lock
LUN mechanism cannot be used in an Extended Distance cluster.
Single Lock Disk or LUN
A single lock disk or lock LUN should be configured on a power circuit
separate from that of any node in the cluster. For example, using three
power circuits for a two-node cluster is highly recommended, with a
separately powered disk or LUN for the cluster lock. In two-node
clusters, this single lock device must not share a power circuit with