PowerHA SystemMirror (formerly HACMP and PowerHA) is IBM's solution for high-availability clusters on the AIX Unix and Linux for IBM System p platforms and stands for High Availability Cluster Multiprocessing. IBM HACMP was first shipped in 1991.
PowerHA SystemMirror can run on up to 32 computers or nodes, each of which is either actively running an application (active) or waiting to take over should another node fail (passive). Data on file systems can be shared between systems in the cluster.
PowerHA SystemMirror relies heavily on IBM's Reliable Scalable Cluster Technology (RSCT). RSCT includes daemons which are responsible for monitoring the state of the cluster (for example, a node, NIC or network crash) and will coordinate the response to these events. HACMP is an RSCT aware client. RSCT is distributed with AIX.