Managing HP Serviceguard for Linux, Eighth Edition, March 2008

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 47
The operation of the lock LUN is shown in Figure 3-2.
Figure 3-2 Lock LUN Operation
Serviceguard periodically checks the health of the lock LUN and writes
messages to the syslog file if the disk fails the health check. This file
should be monitored for early detection of lock disk problems.
Use of the Quorum Server as a Cluster Lock
The cluster lock in Linux can also be implemented by means of a
quorum server. A quorum server can be used in clusters of any size.
The quorum server software can be configured as a Serviceguard
package, or standalone, but in either case it must run on a system
outside of the cluster for which it is providing quorum services.
The quorum server listens to connection requests from the Serviceguard
nodes on a known port. The server maintains a special area in memory
for each cluster, and when a node obtains the cluster lock, this area is
marked so that other nodes will recognize the lock as “taken.”
If the quorum server is not available when its tie-breaking services are
needed during a cluster re-formation, the cluster will halt.