Managing Serviceguard 14th Edition, June 2007

Planning and Documenting an HA Cluster
Cluster Lock Planning
Chapter 4 145
Planning for Expansion
Bear in mind that a cluster with more than 4 nodes cannot use a lock
disk or lock LUN. Thus, if you plan to add enough nodes to bring the total
to more than 4, you should use a quorum server.
Using a Quorum Server
The Quorum Server is described in detail under “Use of the Quorum
Server as the Cluster Lock” on page 69. See also “Cluster Lock” on
page 65.
A quorum server:
• Can be used with up to 50 clusters, not exceeding 100 nodes total.
• Can support a cluster with any supported number of nodes.
Networking Recommendations for a Quorum Server
• Ideally the Quorum Server and the cluster or clusters it serves
should communicate over a subnet that does not handle other traffic.
This helps to ensure that the Quorum Server is available when it is
needed.
If this is not practical, or if the communication must cover a long
distance (for example, if the Quorum Server is serving an Extended
Distance cluster) heavy network traffic or network delays could
cause Quorum Server timeouts. You can reduce the likelihood of
timeouts by increasing the Quorum Server timeout interval; use the
QS_TIMEOUT_EXTENSION parameter in the cluster configuration file.
See “Specifying a Quorum Server” on page 237.
• If a subnet that connects the Quorum Server to a cluster is also used
for the cluster heartbeat, configure the heartbeat on at least one
other network, so that both Quorum Server and heartbeat
communication are not likely to fail at the same time.
For more information, see the Quorum Server Release Notes and white
papers at: http://www.docs.hp.com -> High Availability.