Quorum node

When changing cluster configuration data or global resource manager replicated global data, RSCT guarantees subsequent discovery of the latest changes by not permitting them unless an N/2 + 1 quorum of all defined nodes participate in committing the changes. The use of quorum nodes reduces this number of required online nodes by applying the N/2 + 1 formula only to a subset of pre-defined nodes, that is, quorum nodes.

Quorum nodes are distinguished from non-quorum nodes by the value of an IsQuorumNode attribute in the PeerNode class. The basis for determining whether a quorum of quorum nodes exists must remain stable for the duration of configuration data updates, global resource manager data updates, or both. This requires coordination between the mechanism for changing quorum node configuration (in the configuration resource manager) and global resource managers. This is addressed by a function of the configuration resource manager and the resource manager framework called quorum coordination, through which the configuration resource manager asks all global resource managers whether they support a quorum set change, and performs the change only if they all reply in the affirmative.

When creating a peer domain, you can use the mkrpdomain command's -f option with a node definition file to specify which nodes are to be quorum nodes and whether they have access to the peer domain's tiebreaker mechanism. In the node definition file, node names that are followed by @Q will be considered as quorum nodes. Node names that are followed by @!Q will be considered as non-quorum nodes. For details about how to specify @Q and @!Q in a node definition file, see the description of the -f option under the mkrpdomain command in the Technical Reference: RSCT for AIX® or the Technical Reference: RSCT for Multiplatforms.

When used in the context of quorum, discussions of nodes in this document refer to quorum nodes.