Oracle RAC Instance Recovery.

1. All nodes available.

2. One or more RAC instances fail.

3. Node failure is detected by any one of the remaining instances.

4. Global Resource Directory(GRD) is reconfigured and distributed among 
   surviving nodes.

5. The instance which first detected the failed instance, reads the failed
   instances redo logs to determine the logs which are needed to be recovered.
   The above task is done by the SMON process of the instance that detected failure.

6. Until this time database activity is frozen, The SMON issues recovery requests
   for all the blocks that are needed for recovery. Once all the blocks are available,
   the other blocks which are not needed for recovery are available for normal processing.

7. Oracle performs roll forward operation against the blocks that were modified by the
   failed instance but were not written to disk using redo log recorded transactions.

8. Once redo logs are applied, uncomitted transactions are rolled back using
   undo tablespace.

9. Database on the RAC in now fully available.