A Red Hat cluster suite, when configured for high availability, attempts to ensure service availability by monitoring other nodes of the cluster. All nodes of the cluster must agree on their configuration and shared services state before the cluster is considered Quorate and services are able to be started.
The primary form of communicating node status is via a network device (commonly Ethernet), although in the case of possible network failure, quorum can be decided through secondary methods such as shared storage or multicast.
Software services, filesystems and network status can be monitored and controlled by the cluster suite, services and resources can be failed over to other network nodes in case of failure.
The cluster suite forcibly terminates a cluster node's access to services or resources to ensure the node and data is in a known state. The node is terminated by removing power or access to the shared storage.
Service locking and control is guaranteed through fencing and STONITH; more recent versions of Red Hat use a distributed lock manager (DLM), to allow fine grained locking and no single point of failure. Earlier versions of the cluster suite relied on GULM (grand unified lock manager) which could be clustered, but still presented a point of failure if the nodes acting as GULM servers were to fail. GULM was last available in Red Hat Cluster Suite 4.
Read more about Red Hat Cluster Suite: Support and Product Life-cycle, History, See Also
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