Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Figure 13-1
Example of a 4-node CVM cluster
Cluster-shareable disks
Cluster-shareable
disk groups
Node 0
(master)
Redundant private network
Redundant
SCSIor Fibre
Channel
connectivity
Node 3
(slave)
Node 2
(slave)
Node 1
(slave)
To the cluster monitor, 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 CVM functionality of VxVM requires that one node act as the master
node; all other nodes in the cluster are slave nodes. Any node is capable of being
the master node, and it is responsible for coordinating certain VxVM activities.
In this example, node 0 is configured as the CVM master node and nodes 1, 2 and
3 are configured as CVM slave nodes. The nodes are fully connected by a private
network and they are also separately connected to shared external storage (either
disk arrays or JBODs: just a bunch of disks) via SCSI or Fibre Channel in a Storage
Area Network (SAN).
In this example, each node has two independent paths to the disks, which are
configured in one or more cluster-shareable disk groups. Multiple paths provide
resilience against failure of one of the paths, but this is not a requirement for
cluster configuration. Disks may also be connected by single paths.
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 were used, its failure would be indistinguishable from node failure—a
condition known as network partitioning.
427Administering cluster functionality (CVM)
Overview of clustering