Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Understanding Serviceguard Software Components
How the Cluster Manager Works
Chapter 3 43
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. The quorum server process runs on a machine 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.”
A quorum server can be used in clusters of any size. In a two-node
cluster, you are required to configure a quorum server or lock LUN. If
communications are lost between these two nodes, the node that obtains
the cluster lock will take over the cluster and the other node will perform
a reboot.
If the quorum server is not available when its tie-breaking services are
needed during a cluster re-formation, the cluster will halt.