To protect your cluster from a preexisting network partition, VCS uses the concept of seeding. Seeding 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. However, if you have I/O fencing enabled in your cluster, you can still configure GAB to automatically seed the cluster even when some cluster nodes are unavailable.
See the Veritas Cluster Server Administrator's Guide.