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Oracle Cluster Registry

The Oracle Cluster Registry (OCR) contains cluster and database configuration and state information for Oracle 10g RAC and CRS. This is roughly analogous to the main.cf file and in-memory configuration in VCS. However, only one process performs I/O to the OCR file on disk.

The information maintained in the OCR includes:

• The list of nodes
• The mapping of database instances to nodes
• CRS application resource profiles
• Resource profiles that define the properties of resources under CRS control
• Rules that define dependencies between the CRS resources
• The current state of the cluster

The OCR data exists on a shared raw volume or a cluster file system that is accessible to each node. This requires approximately 100 MB of disk space.

You can specify redundant storage for the OCR to protect against failures. CRS faults nodes if the OCR is not accessible because of corruption or disk failure. Oracle automatically backs up OCR data. You can also export the OCR contents before making configuration changes in CRS. This way, if you encounter configuration problems and are unable to restart CRS, you can restore the original contents.