Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 6 - Install, Configure and Database Creation

Cluster Software

Cluster software protects against the conditions of split-brain and amnesia. As noted in an earlier section, split-brain condition occurs when communication between nodes is lost and the cluster becomes partitioned into sub-clusters, each believing that it is the only partition. Amnesia occurs when the cluster restarts after a shutdown using cluster configuration data older than at the time of the shutdown. The changes in cluster membership drive the cluster reconfiguration sequence that may, in turn, result in services being migrated from failed or faulty nodes to healthy ones.

CRS - Cluster Ready Services

Oracle 10g introduces Cluster Ready Services (CRS), which provides many system management services and interacts with the vendor clusterware to coordinate cluster membership information. It provides the cluster software, sometimes called the Oracle OSD Clusterware.

The OUI installs CRS on each node on which the OUI detects that vendor clusterware is running. In addition, the CRS home is distinct from the RAC-enabled Oracle Home. The CRS home can be shared either by one or more nodes, or by private to each node, depending on the settings when you run the OUI. When vendor clusterware is present, CRS interacts with the vendor clusterware to coordinate cluster membership information.