Managing HP Serviceguard for Linux Ninth Edition, April 2009

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.
The operation of the quorum server is shown in Figure 3-3. When there is a loss of
communication between node 1 and node 2, the quorum server chooses one node (in
this example, node 2) to continue running in the cluster. The other node halts.
46 Understanding Serviceguard Software Components