Quorum node
IBM® i clustering technology is used within the Db2® Mirror configuration to manage IASP relationships, to differentiate between communication and node failures, and to store key data, called quorum data, between the nodes. Quorum data is kept synchronized between the nodes by the clustering technology so that when a node or IASP resumes after an outage, the correct replication state can be determined.
Adding a third node, called a quorum node, into the Db2 Mirror configuration provides an extra layer of resiliency. If both Db2 Mirror nodes are inactive, a quorum node is required to resolve which node has the most current data and should be set to TRACKING state. Without a quorum node, both nodes would be set to BLOCKED state when they start, and the Db2 Mirror administrator would be required to make the determination and force one of the nodes to a TRACKING state.
A node which is only used to store quorum data does not require a Db2 Mirror license. If a third node is already used for the Db2 Mirror GUI, or if a third node is part of a disaster recovery configuration, that node can be used as the quorum node. A quorum node does not require large amounts of CPU, memory, or disk if its only function is to be the quorum node. A node can only be in one IBM i cluster, however, so two or more Db2 Mirror configurations cannot share the same quorum node.
A quorum node can be defined as part of the initial Db2 Mirror configuration. To view the current configuration, add a quorum node after initial configuration, or change the existing quorum node, from the Setup tab on the left side, choose Manage Cluster as shown below. A node can be added to the cluster, or an existing third node can be updated or deleted.
You can also use the db2mtool Qshell command to list the cluster nodes, add or remove a node, or change the IP address of a node. The command and its parameters are documented in Cluster actions.
If the IBM PowerHA® SystemMirror® for i product (5770-HAS) is installed, there are PowerHA commands to Display Cluster Information (DSPCLUINF), Add Cluster Node Entry (ADDCLUNODE), and Change Cluster Node Entry (CHGCLUNODE). The Work with Cluster (WRKCLU) command can be used to display and update the nodes in the cluster.