Shut down the database instance.

SHUTDOWN IMMEDIATE
An open database must first be closed and any associated instances shut down before you can switch the database archiving mode. You cannot change the mode from ARCHIVELOG to NOARCHIVELOG if any data files need media recovery.

Back up the database.

Before making any major change to a database, always back up the database to protect against any problems. This will be your final backup of the database in NOARCHIVELOG mode and can be used if something goes wrong during the change to ARCHIVELOG mode. See Oracle Database Backup and Recovery User's Guide for information about taking database backups.

Edit the initialization parameter file to include the initialization parameters that specify the destinations for the archived redo log files (see "Setting Initialization Parameters for Archive Destinations").

Start a new instance and mount, but do not open, the database.

STARTUP MOUNT
To enable or disable archiving, the database must be mounted but not open.

Change the database archiving mode. Then open the database for normal operations.

ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;
Shut down the database.

SHUTDOWN IMMEDIATE
Back up the database.