Backing Up a Database in NOARCHIVELOG Mode:
1.Log into RMAN
2.Shutdown immediate from RMAN
3.Startup mount from RMAN
4.backup database
5.alter database open
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If a database runs in NOARCHIVELOG mode, then the only valid database backup is a consistent backup. For the backup to be consistent, the database must be
mounted after a consistent shutdown. No recovery is required after restoring the backup.
To make a consistent database backup:
1. Start RMAN and connect to a target database.
2. Shut down the database consistently and then mount it. For example, enter the following commands to guarantee that the database is in a consistent state for a
backup:
RMAN> SHUTDOWN IMMEDIATE;
RMAN> STARTUP FORCE DBA;
RMAN> SHUTDOWN IMMEDIATE;
RMAN> STARTUP MOUNT;

3. Run the BACKUP DATABASE command.
For example, enter the following command at the RMAN prompt to back up the database to the default backup device:
RMAN> BACKUP DATABASE;
The following variation of the command creates image copy backups of all data files in the database:
RMAN> BACKUP AS COPY DATABASE;
4. Open the database and resume normal operations.
The following command opens the database:
RMAN> ALTER DATABASE OPEN;