•We can use RMAN DUPLICATE database command in order to create a new database with the identical copy of original database or subset of the tablespaces of the original database.
•In order to duplicate database, we must need one auxiliary instance. The auxiliary channel of the auxiliary instance starts a server session on the duplicate host and performs the principle work of duplication database.
•We need backup and archived redo logs of primary database and we will perform duplication with this backups.
•In order to perform duplication, the auxiliary instance must be started in NOMOUNT state and then the auxiliary channel restores the backup of the primary database in to the duplicate database.
•All backups and archived redo logs used for creating and recovering duplicate database must be accessible by the server session on the duplicate host.
•While database duplication by RMAN, RMAN automated several steps.
•Creates control file for the duplicate database.
•Restores the target datafiles to the duplicate database and performs incomplete recovery by using all available incremental backups and archived redo logs.
•Shuts down and starts the auxiliary instance.
•Opens the duplicate database with the RESETLOGS option after incomplete recovery to create the online redo logs.
•RMAN generates a new, unique DBID for the duplicate database.
•It is good to remember that During duplication, RMAN must perform incomplete recovery because the online redo logs in the target are not backed up and cannot be applied to the duplicate database.
The farthest that RMAN can go in recovery of the duplicate database is the most recent redo log archived by the target database.