Installation guide

10 Chapter 1:Introduction to Red Hat Cluster Manager
the two systems from simultaneously accessing the same data and corrupting it. Although not
required, it is recommended that power switches are used to guarantee data integrity under all
failure conditions. Watchdog timers are an optional variety of power control to ensure correct
operation of service failover.
• Cluster administration user interface
A user interface simplifies cluster administration and enables an administrator to easily create,
start, stop, relocate services, and monitor the cluster.
• Multiple cluster communication methods
To monitor the health of the other cluster system, each cluster system monitors the health of the
remote power switch, if any, and issues heartbeat pings over network and serial channels to mon-
itor the health of the other cluster system. In addition, each cluster system periodically writes a
timestamp and cluster state information to two quorum partitions located on shared disk storage.
System state information includes whether the system is an active cluster member. Service state
information includes whether the service is running and which cluster system is running the ser-
vice. Each cluster system checks to ensure that the other system’s status is up to date.
To ensure correct cluster operation, if a system is unable to write to both quorum partitions at
startup time, it will not be allowed to join the cluster. In addition, if a cluster system is not updating
its timestamp, and if heartbeats to the system fail, the cluster system will be removed from the
cluster.