Managing Serviceguard Fifteenth Edition, reprinted May 2008

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 370
When a node obtains the cluster lock, this area is marked so that other
nodes will recognize the lock as “taken.”
The operation of the lock disk or lock LUN is shown in Figure 3-2.
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.