Managing Serviceguard Eighteenth Edition, September 2010

Figure 3-3 Quorum Server Operation
The Quorum Server runs on a separate system, and can provide quorum services for
multiple clusters.
IMPORTANT: For more information about the Quorum Server, see the latest version
of the HP Serviceguard Quorum Server release notes at www.hp.com/go/
hpux-serviceguard-docs -> HP Serviceguard Quorum Server Software.
No Cluster Lock
Normally, you should not configure a cluster of three or fewer nodes without a cluster
lock. In two-node clusters, a cluster lock is required. You may consider using no cluster
lock with configurations of three or more nodes, although the decision should be
affected by the fact that any cluster may require tie-breaking. For example, if one node
in a three-node cluster is removed for maintenance, the cluster re-forms as a two-node
cluster. If a tie-breaking scenario later occurs due to a node or communication failure,
the entire cluster will become unavailable.
In a cluster with four or more nodes, you may not need a cluster lock since the chance
of the cluster being split into two halves of equal size is very small. However, be sure
to configure your cluster to prevent the failure of exactly half the nodes at one time.
For example, make sure there is no potential single point of failure such as a single
LAN between equal numbers of nodes, and that you don’t have exactly half of the
nodes on a single power circuit.
What Happens when You Change the Quorum Configuration Online
You can change the quorum configuration while the cluster is up and running. This
includes changes to the quorum method (for example from a lock disk to a Quorum
66 Understanding Serviceguard Software Components