A cluster is a loosely coupled collection of independent
systems (nodes) that are organized into a network for sharing the
resources and communicating with each other. If a cluster node is
not able to provide services, PowerHA® SystemMirror defines
relationships among the operating systems so that the peer cluster
nodes provide those services.
Before you start, you must complete the following prerequisites:
- Install PowerHA SystemMirror software
on all the nodes that you want to include in the cluster.
- Ensure that all nodes that you want to include in the cluster
meet the following requirements:
- They have the same AIX® version
installed on them.
- They have the same version and edition of the PowerHA SystemMirror installed
on them.
- They have at least one storage disk in common among them to be
used exclusively for the cluster repository. This repository contains
configuration and other important data that all nodes need to be able
to access.
- Connect and configure all the IP network interfaces.
- Discover all nodes in your subnetwork by using the Discovery task
in the IBM® Systems Director.
- Request access to nodes that have a status of no access by
using the Request Access task in the IBM Systems Director.
- Collect information to define an active communication path to
the takeover node.
The wizard automatically discovers and configures the various communication
paths between the local node and the takeover node. If the local node
and the takeover node have IP aliases associated with them, and the
aliases are reachable from the local node, the wizard automatically
configures the aliases as
PowerHA SystemMirror persistent
IP addresses.
Note: You can also supply specific values for persistent
IP addresses for the local node and the takeover node, if you prefer.
If you are using
PowerHA SystemMirror 7.1 Enterprise Edition,
the nodes that you want to include in the cluster must meet the following
additional requirements:
- The local node must have an active communication path to the takeover
node.
- The local node and the takeover node must have the required filesets
installed on them.
Note: 
Review the
PowerHA SystemMirror release_notes file
in the
/usr/es/sbin/cluster/ directory for a
full list of filesets, further instructions, and the latest information
on requirements or known issues.

For more information about creating clusters, see the Create a Cluster topic in the AIX information center.