VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Cluster Functionality Overview
Chapter 7302
configuration of VxVM is required, apart from the cluster configuration
requirements of MC/ServiceGuard.
Node initialization is effected through the cluster manager startup
procedure, which brings up the various cluster components (such as
VxVM with cluster support, the cluster manager, and a distributed lock
manager) on the node. Once it is complete, applications may be started.
The system administrator invokes the cluster manager startup
procedure on each node to be joined to the cluster.
For VxVM in a cluster environment, initialization consists of loading the
cluster configuration information and joining the nodes in the cluster.
The first node to join becomes the master node, and later nodes (slaves)
join to the master. If two nodes join simultaneously, VxVM software
chooses the master. Once the join for a given node is complete, that node
has access to the shared disks.
Cluster Reconfiguration
Any time there is a change in the state of the cluster (in the form of a
node leaving or joining), a cluster reconfiguration occurs. The cluster
manager for each node monitors other nodes in the cluster and calls the
vxclustd cluster reconfiguration utility when there is a change in
cluster membership.The vxclustd utility coordinates cluster
reconfigurations and provides communication between VxVM and the
cluster manager. The cluster manager and the vxclustd utility work
together to ensure that each step in the cluster reconfiguration is
completed in the correct order.
During a cluster reconfiguration, I/O to shared disks is suspended. It is
resumed when the reconfiguration completes. Applications may
therefore appear to be frozen for a short time.
If other operations (such as Volume Manager operations or recoveries)
are in progress, the cluster reconfiguration may be delayed until those
operations have completed. Volume reconfigurations (described later) do
not take place at the same time as cluster reconfigurations. Depending
on the circumstances, an operation may be held up and restarted later.
In most cases, cluster reconfiguration takes precedence. However, if the
volume reconfiguration is in the commit stage, it will complete first.
For more information on cluster reconfiguration, see “vxclustd Daemon”.