Oracle Database Tips by Donald Burleson

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

CRS - Cluster Ready Services

For Oracle10g on Linux and Windows-based platforms, CRS co-exists with but does not inter-operate with vendor clusterware. You may use vendor clusterware for all UNIX-based operating systems except for Linux. Even though, many of the Unix platforms have their own clusterware products, you need to use the CRS software to provide the HA support services. CRS (cluster ready services) supports services and workload management and helps to maintain the continuous availability of the services. CRS also manages resources such as virtual IP (VIP) address for the node and the global services daemon.

The Oracle Cluster Registry (OCR) contains cluster and database configuration information for Real Application Clusters Cluster Ready Services (CRS), including the list of nodes in the cluster database, the CRS application, resource profiles, and the authorizations for the Event Manager (EVM). The OCR can reside in a file on a cluster file system or on a shared raw device. When you install Real Application Clusters, you specify the location of the OCR.

CRS helps to package a set of application work under CRS control and access the RAC database. The application resource profile defines the resources with which you manage the RAC. Prior to the 10g release, the cluster manager implementations on some platforms were referred to as "Cluster Manager". In Oracle10g, Cluster Synchronization Services (CSS) is the cluster manager on all platforms. The Oracle Cluster Synchronization Service Daemon (OCSSD) performs this function on UNIX-based platforms.