Quorumless domain

A peer domain can be configured to operate without quorum requirements. When normal (strong) quorum is disabled, the IsQuorumNode attribute is not used. The number of nodes that is required to satisfy the startup, configuration, and operational quorum is always one. However, if domain partitioning happens, a tiebreaker is always used to resolve operational quorum. When operating without quorum restrictions, configuration changes can be made independently to domain partitions. When the partitions rejoin, the configuration changes that are made to one partition are overwritten by the other partition.

During the start of a peer domain that is configured to be quorumless, the configuration resource manager tries to contact all of the cluster nodes to discover the configuration that contains the most recent changes. The QuorumLessStartupTimeout attribute of the IBM.PeerNode resource class determines the maximum time that is spent in attempting to contact the remote nodes while bringing the domain online. After all of the nodes are contacted or the timeout expires, the domain comes online with the most recently determined configuration among all of the reachable nodes. Nodes that join the domain later conform to the configuration of the online domain. Although the configuration resource manager attempts to locate the most recent peer domain configuration, there is no assurance which configuration might be chosen if changes are made while the cluster is partitioned. The configuration can be reverted if a node with a later version is inactive or unreachable.

Likewise, the configuration of global resource managers that are operating in a quorumless peer domain can be reverted when a node or domain is brought online. Global resource managers that are running in a quorumless domain come operational with the configuration that is associated with the first node to become online. This type of quorum is therefore only recommended for specific environments where the configuration data is static or can be rediscovered by the resource managers; for example, PowerHA® or the shared storage pool in Cluster-Aware AIX® (CAA) domains.