2.2.1 The vxclust Command

vxclust is not a portable utility. Although vxclust performs the same or similar operations in relation to the SSVM, it needs to be modified or rewritten to operate with each particular cluster manager.

vxclust is the volume manager cluster reconfiguration utility. vxclust coordinates changes in cluster membership and provides communication between the cluster manager and CVM. Whenever there is a cluster reconfiguration, vxclust is called by the cluster manager. vxclust notifies the volume manager kernel and the vxconfigd daemon whenever cluster reconfiguration takes place.

Every time there is a cluster reconfiguration, every node currently in the cluster runs the vxclust utility at each of several well-orchestrated steps. Cluster manager facilities ensure that the same step is executed on all nodes at the same time. A given step only starts when the previous one has completed on all nodes. At each step in the reconfiguration, vxclust determines what CVM should do next. After informing CVM of its next action, vxclust waits for the outcome (success, failure, or retry) and communicates that to the cluster manager.

If a node does not respond to a vxclust request within a specific timeout period, that node aborts. vxclust then decides whether to restart the reconfiguration or give up, depending on the circumstances. If the cause of the reconfiguration is a local, uncorrectable error, vxclust stops the action. If a node cannot complete an operation because another node has left, the surviving node times out. In this case, vxclust requests a reconfiguration with the expectation that another node will leave. If no other node leaves, vxclust will cause the local node to leave.

If a reconfiguration step fails, vxclust returns an error to the cluster manager. The cluster manager can decide to abort the node, causing its immediate departure from the cluster. Any I/O in progress to the shared disk fails and access to the shared disks is stopped.

vxclust decides what actions to take when it is informed of changes in the cluster. If a new master node is required (due to failure of the previous master), vxclust determines which node becomes the new master.