Also known as the VCS engine, HAD is responsible for the following functions:
The local engine also receives information from the other cluster members to update its view of the cluster. HAD operates as a replicated state machine (RSM). The engine that runs on each node has a completely synchronized view of the resource status on each node. Each instance of HAD follows the same code path for corrective action, as required.
The RSM is maintained through the use of a purpose-built communications package. The communications package consists of the protocols Low Latency Transport (LLT) and Group Membership Services and Atomic Broadcast (GAB).