VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Cluster Functionality Overview
Chapter 7 299
How Cluster Volume Management Works
The Volume Manager cluster feature works together with an
externally-provided cluster manager, which is a daemon that informs
VxVM of changes in cluster membership. Each node starts up
independently and has its own copies of the operating system, VxVM
with cluster support, and the cluster manager. When a node joins a
cluster, it gains access to shared disks. When a node leaves a cluster, it
no longer has access to those shared disks. The system administrator
joins a node to a cluster by starting the cluster manager on that node.
The following figure illustrates a simple cluster arrangement. All of the
nodes are connected by a network. The nodes are then connected to a
cluster-shareable disk group. To the cluster manager, all nodes are the
same. However, the Volume Manager cluster feature requires that one
node act as the master node; the other nodes are slave nodes. The
master node is responsible for coordinating certain Volume Manager
activities. VxVM software determines which node performs the master
function (any node is capable of being a master node); this role only
changes if the master node leaves the cluster. If the master leaves the
cluster, one of the slave nodes becomes the new master. In Figure 7-1,
Example of a 4-Node Cluster,, Node 1 is the master node and Node 2,
Node 3, and Node 4 are the slave nodes.