Red Hat CLUSTER SUITE FOR ENTERPRISE LINUX 4.6 Overview page 16

Chapter 1. Red Hat Cluster Suite Overview
• Configured with one GULM server — Quorum equals one GULM server.
• Configured with three GULM servers — Quorum equals two GULM servers.
• Configured with five GULM servers — Quorum equals three GULM servers.
The cluster manager keeps track of membership by monitoring heartbeat messages from other
cluster nodes. When cluster membership changes, the cluster manager notifies the other
infrastructure components, which then take appropriate action. For example, if node A joins a
cluster and mounts a GFS file system that nodes B and C have already mounted, then an
additional journal and lock management is required for node A to use that GFS file system. If a
cluster node does not transmit a heartbeat message within a prescribed amount of time, the
cluster manager removes the node from the cluster and communicates to other cluster
infrastructure components that the node is not a member. Again, other cluster infrastructure
components determine what actions to take upon notification that node is no longer a cluster
member. For example, Fencing would fence the node that is no longer a member.
Figure 1.2. CMAN/DLM Overview
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