Symantec 5 manual About preexisting network partitions, About VCS seeding

16Introducing Veritas Cluster Server About VCS basics

Figure 1-3illustrates a two-node VCS cluster where the nodes galaxy and nebula have two private network connections.

Figure 1-3 Two Ethernet connections connecting two nodes

VCS private network: two ethernet connections

galaxy

Shared disks

nebula

Public network

About preexisting network partitions

A preexisting network partition refers to a failure in the communication channels that occurs while the systems are down and VCS cannot respond. When the systems start, VCS is vulnerable to network partitioning, regardless of the cause of the failure.

About VCS seeding

To protect your cluster from a preexisting network partition, VCS uses a seed. A seed is a function of GAB that determines whether or not all nodes have joined a cluster. For this determination, GAB requires that you declare the number of nodes in the cluster. Note that only seeded nodes can run VCS.

GAB automatically seeds nodes under the following conditions:

■An unseeded node communicates with a seeded node

■All nodes in the cluster are unseeded but can communicate with each other

When the last system starts and joins the cluster, the cluster seeds and starts VCS on all nodes. You can then bring down and restart nodes in any combination. Seeding remains in effect as long as at least one instance of VCS is running somewhere in the cluster.

Perform a manual seed to run VCS from a cold start when one or more systems of the cluster are unavailable. VCS does not start service groups on a system until it has a seed.