Even in single-site configurations, the same last-man-standing code will be
implemented. If I have a single site with only two nodes left in the cluster and no
witness, one of the nodes would lose its vote. Let’s look in more detail at this “last two
votes standing” scenario. as shown in Figure 7.7, which continues with the scenario we
looked at in Figure 7.4. Note that in this example, there is no witness, which would not
be best practice.
If node B now has a failure, the cluster continues running on node A, because node
A has the last remaining vote and has quorum majority (it has the single vote, so it
has 100 percent of the vote and therefore > 50 percent).
If node A has a failure and shuts down, then node B’s cluster service will stop,
because node A had the only vote and therefore node B has no vote and cannot
make quorum.
If a communication failure happens between node A and node B, then node A will
keep running with quorum majority while node B’s cluster service will stop.
If node A shuts down cleanly, then before it shuts down it will transfer its vote to
node B, which means that the cluster will continue running on node B.Figure 7.7 Two remaining nodes in a cluster
With all of these new technologies, it’s hard for the cluster to lose quorum. To lose
quorum, the cluster would have to simultaneously lose more than half the number of
votes, in which case you should shut down the cluster to protect the integrity of the
services.
This brings us to forcing quorum. Consider a remote site that has a minority number
of votes but in a disaster the cluster service must be started. Even in normal
circumstances, at times nodes could be lost and the cluster service must be started
even without quorum majority. This is known as Forced Quorum, and it allows the
cluster to start without a majority of votes. When a cluster is started in Forced
Quorum mode, it stays in that mode until a majority of nodes is available as they
come online again, at which point the cluster automatically switches from Forced
Quorum mode to the normal mode. To start the cluster in Forced Quorum mode,
perform one of the following on one node that will be part of the Forced Quorum
partition:
Run the command Start-ClusterNode -ForceQuorum.
Run the command Net start clussvc /ForceQuorum.