Managing HP Serviceguard for Linux, Tenth Edition, September 2012

NOTE: The lock LUN is dedicated for use as the cluster lock, and, in addition, HP
recommends that this LUN comprise the entire disk; that is, the partition should take up
the entire disk.
The complete path name of the lock LUN is identified in the cluster configuration file.
The operation of the lock LUN is shown in Figure 7.
Figure 7 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 8. 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.
How the Cluster Manager Works 41