Managing HP Serviceguard A.11.20.10 for Linux, December 2012

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.
3.2.9 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.
Figure 8 Quorum Server Operation
A quorum server can provide quorum services for multiple clusters. Figure 9 illustrates quorum
server use across four clusters.
3.2 How the Cluster Manager Works 39