Veritas Storage Foundation 5.1 SP1 for Oracle RAC Administrator"s Guide (5900-1512, April 2011)

Port a gen 7e6e7e01 membership 01
In this case, 7e6e7e01 indicates the “membership generation number” and 01
corresponds to the cluster’s “node map”. All nodes present in the node map reflects
the same membership ID as seen by the following command:
# gabconfig -a | grep "Port a"
The semi-colon is used as a placeholder for a node that has left the cluster. In the
following example, node 0 has left the cluster:
# gabconfig -a | grep "Port a"
Port a gen 7e6e7e04 membership ;1
When the last node exits the port “a” membership, there are no other nodes to
increment the membership ID. Thus the port “a” membership ceases to exist on
any node in the cluster.
When the last and the final system is brought back up from a complete cluster
cold shutdown state, the cluster will seed automatically and form port “a”
membership on all systems. Systems can then be brought down and restarted in
any combination so long as at least one node remains active at any given time.
The fact that all nodes share the same membership ID and node map certifies that
all nodes in the node map participates in the same port “a” membership. This
consistency check is used to detect “split-brain” and “pre-existing split-brain”
scenarios.
Split-brain occurs when a running cluster is segregated into two or more partitions
that have no knowledge of the other partitions. The pre-existing network partition
is detected when the "cold" nodes (not previously participating in cluster) start
and are allowed to form a membership that might not include all nodes (multiple
sub-clusters), thus resulting in a potential split-brain.
Note: Symantec I/O fencing prevents data corruption resulting from any split-brain
scenarios.
Manual GAB membership seeding
It is possible that one of the nodes does not come up when all the nodes in the
cluster are restarted, due to the "minimum seed requirement" safety that is
enforced by GAB. Human intervention is needed to safely determine that the other
node is in fact not participating in its own mini-cluster.
The following should be carefully validated before manual seeding, to prevent
introducing split-brain and subsequent data corruption:
237Prevention and recovery strategies
Manual GAB membership seeding