The SET CLUSTER/EXPECTED_VOTES command enables you to adjust the total
number of expected votes in the cluster. Set this value equal to the
number of votes contributed by each node plus the number of votes
contributed by the cluster quorum disk. The system will automatically
calculate the value of the cluster quorum from the total number of
expected votes in the cluster.
You can specify the expected total votes value as part of the SET
CLUSTER/EXPECTED_VOTES command string. If you enter the command without
specifying a value for expected votes, the system calculates the value
for you, using the following formula:
EXPECTED_VOTES=(NODE1_VOTES+NODE2_VOTES+...)+QUORUM_DISK_VOTES
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NODEn_VOTES is the value of the system parameter VOTES for
each node in the cluster and QUORUM_DISK_VOTES is the value of the
system parameter QDSKVOTES.
When you enter the SET CLUSTER/EXPECTED_VOTES command without
specifying a value, the system assumes that all nodes that are expected
to be in the cluster are currently members.
In general, you use the SET CLUSTER/EXPECTED_VOTES command only when a
node is leaving the cluster for an extended period of time. Under
normal circumstances, quorum is not reduced when a node leaves the
cluster, because it is assumed that the node may be rebooted and rejoin
the cluster. If a node is removed and is unable to rejoin the cluster
within a reasonable period of time (for example, if a node crashes due
to a hardware problem and cannot rejoin the cluster for several days),
the quorum for the cluster can safely be reduced by lowering the total
expected votes until that node rejoins.
The purpose of a cluster quorum is to eliminate any possibility of the
cluster partitioning into separate clusters and simultaneously
accessing the same resources (such as disks). If the sum of the votes
for all members of the cluster is smaller than the cluster quorum, all
nodes will block activity until new nodes join to increase the vote
total. Lowering the quorum value (by reducing the value of the total
expected votes) when one or more nodes leave the cluster for long
periods of time reduces this possibility.
Note that no matter what value you specify for the SET
CLUSTER/EXPECTED_VOTES command, you cannot increase quorum to a value
that is greater than the number of the votes present, nor can you
reduce quorum to a value that is half or fewer of the votes present.
When you enter the SET CLUSTER/EXPECTED_VOTES command, either with or
without an expected votes value specified, the system responds with a
message indicating the new value that was actually set. Note that you
need to enter this command only on one node in the cluster, because the
new value for total expected votes is propagated through the cluster.
This new expected votes value should then be stored in the system
parameter EXPECTED_VOTES on each node, so that it remains in effect
after the nodes reboot.
When a node that was previously a member of the cluster is ready to
rejoin, you should increase the system parameter EXPECTED_VOTES to its
original value before bringing the node back to the cluster. Note that
you do not need to use the SET CLUSTER/EXPECTED_VOTES command to
increase the number of expected votes, because the expected votes value
will be increased automatically when the node rejoins the cluster.
