Managing Serviceguard 11th Edition, Version A.11.16, Second Printing June 2004

Planning and Documenting an HA Cluster
General Planning
Chapter 4126
Planning for Expansion
When you first set up the cluster, you indicate a set of nodes and define a
group of packages for the initial configuration. At a later time, you may
wish to add additional nodes and packages, or you may wish to use
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:
• Set the Maximum Configured Packages parameter (described later
in this chapter in the “Cluster Configuration Planning” section) high
enough to accommodate the additional packages you plan to add.
Keep in mind that adding package capacity uses memory resources
(100 KB per package).
• Plan SCSI bus cabling to allow the addition of more disk hardware
for shared data storage if needed. You should attach inline SCSI
terminator cables to SCSI ports that you intend to use for additional
devices. This allows you to add them while the bus is still active.
• 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 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.