Managing Serviceguard Fifteenth Edition, reprinted May 2008

Planning and Documenting an HA Cluster
General Planning
Chapter 4 133
additional disk hardware for shared data storage. If you intend to
expand your cluster without the need to bring it down, careful planning
of the initial configuration is required. Use the following guidelines:
• Remember the rules for cluster locks when considering expansion. A
one-node cluster does not require a cluster lock. A two-node cluster
must have a cluster lock. In clusters larger than 3 nodes, a cluster
lock is strongly recommended. If you have a cluster with more than 4
nodes, you can use a quorum server but a cluster lock disk is not
allowed.
• Networks should be pre-configured into the cluster configuration if
they will be needed for packages you will add later while the cluster
is running.
• Resources monitored by EMS (Event Monitoring Service) should be
pre-configured into the cluster configuration if they will be needed
for packages you will add later while the cluster is running. Once a
resource dependency is configured for any package in the cluster, it
will always be available for later packages to use. However, you
cannot add a never-before-configured resource to a package while the
package is running.
Refer to the chapter on “Cluster and Package Maintenance” for more
information about changing the cluster configuration dynamically, that
is, while the cluster is running.