About Putting the Oracle RAC Database Instances into the Correct State

Recovery of a failed instance in Oracle RAC is automatic. If an Oracle RAC database instance fails, then a surviving database instance processes the online redo logs generated by the failed instance to ensure that the database contents are in a consistent state. When recovery completes, Oracle Clusterware attempts to restart the failed instance automatically.

Media recovery is a manual process that occurs while a database is closed. A media failure is the failure of a read or write operation of a disk file required to run the database, due to a physical problem with the disk such as a head malfunction. Any database file can be vulnerable to a media failure. If a media failure occurs, then you must perform media recovery to restore and recover the damaged database files. Media recovery is always done by one instance in the cluster.

Before starting media recovery, the instance that will be performing the recovery should be started in MOUNT mode. The other instances should be started in NOMOUNT mode.