Veritas Storage Foundation 5.0.1 Cluster File System Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

IMPORTANT: The cluster functionality of VxVM is supported only when used in conjunction
with the cmvx daemon.
Figure 4-1: “Example of a 4-Node Cluster”, illustrates a simple cluster arrangement consisting
of four nodes with similar or identical hardware characteristics (CPUs, RAM and host adapters),
and configured with identical software (including the operating system). The nodes are fully
connected by a private network and they are also separately connected to shared external storage
(either disk arrays or JBODs) via FibreChannel. Each node has two independent paths to these
disks, which are configured in one or more cluster-shareable disk groups.
The private network allows the nodes to share information about system resources and about
each other’s state. Using the private network, any node can recognize which other nodes are
currently active, which are joining or leaving the cluster, and which have failed. The private
network requires at least two communication channels to provide redundancy against one of
the channels failing. If only one channel is used (a condition known as network partitioning), its
failure will be indistinguishable from node failure.
Figure 4-1 Example of a 4-Node 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
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.
30 Cluster Volume Manager Administration