The Cluster Ready Services (CRS) technology stack leverages several processes to manage various services. It manages resource availability, high availability, and cluster operations within Oracle Grid Infrastructure. Cluster Ready Services is the primary program for managing high availability operations in a cluster.
The CRSD manages cluster resources based on the configuration information that is stored in OCR for each resource. This includes start, stop, monitor, and failover operations. The CRSD process generates events when the status of a resource changes. When you have Oracle RAC installed, the CRSD process monitors the Oracle database instance, listener, and so on, and automatically restarts these components when a failure occurs.
Even though CRS and High Availability Services have programs named the same they are distinctly different, such as: oraagent and orarootagent. To know more about the Oracle Clusterware platform, refer to the Overview of Oracle Clusterware Platform-Specific Software Components.