Administrator's Guide

Cluster Volume Manager Administration
Overview of Cluster Volume Management
Chapter 4
41
Figure 4-1 Example of a 4-Node Cluster
To the cmvx daemon, all nodes are the same. VxVM objects configured within shared disk
groups can potentially be accessed by all nodes that join the cluster. However, the cluster
functionality of VxVM requires that one node act as the master node; all other nodes in
the cluster are secondary nodes. Any node is capable of being a master node. The master
node is responsible for coordinating certain VxVM activities.
NOTE You must run commands that configure or reconfigure VxVM objects on the master node.
Tasks that must be initiated from the master node include setting up shared disk
groups, creating and reconfiguring volumes, and performing snapshot operations.
VxVM designates the first node to join a cluster as the master node for that cluster. If the
master node leaves the cluster, one of the secondary nodes is chosen to be the new
master node. In Figure 4-1, Example of a 4-Node Cluster, node 0 is the master node and
nodes 1, 2 and 3 are secondary nodes.
Private and Shared Disk Groups
Two types of disk groups are defined:
• Private disk groups (belong to only one node). A private disk group is only imported
by one system. Disks in a private disk group may be physically accessible from one or
more systems, but access is restricted to one system only. The boot disk group
(usually aliased by the reserved disk group name bootdg) is always a private disk
group.
• Shared disk groups (shared by all nodes). A shared (or cluster-shareable) disk group
is imported by all cluster nodes. Disks in a shared disk group must be physically
accessible from all systems that may join the cluster.
Redundant
Fibre Channel
Connectivity
Cluster-Shareable
Disks
Redundant Private Network
Node 0
Master
Node 1
Slave
Node 2
Slave
Node 3
Slave
Cluster-Shareable
Disk Groups