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Figure 1-3 illustrates 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
Shared disks
Public network
galaxy nebula
About preexisting network partitions
Apreexistingnetworkpartition referstoafailurein thecommunicationchannels
thatoccurswhilethe systemsaredown andVCScannotrespond. Whenthesystems
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
Whenthe lastsystem starts andjoins thecluster, thecluster seeds andstarts 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 doesnot start service groups on a system until
it has a seed.
Introducing Veritas Cluster Server
About VCS basics
16