Controlfile and Server parameter file (spfile) autobackup

RMAN can be configured to automatically backup the control file and server parameter file (spfile) whenever the database structure in the control file changes and whenever a backup record is added. The autobackup feature enables RMAN to recover the database even if the current control file, catalog, and server parameter file are lost.

The RMAN can search the autobackup path and restore the server parameter file from backup. Once the instance is started with restored spfile, use RMAN to restore the controlfile from autobackup. After you mount the DB using restored control file, use RMAN repository information from control file to restore and recover the data files.

You can turn ON or OFF the autobackup feature by using the following commands:
RMAN>CONFIGURE CONTROLFILE AUTOBACKUP ON;
RMAN>CONFIGURE CONTROLFILE AUTOBACKUP OFF;

If control file autobackups is ON and the backup includes datafile 1, RMAN writes the control file and SPFILE to a separate backup set. If autobackup is OFF and the backup includes datafile 1, then RMAN includes the current control file and SPFILE in the same backup set as the datafiles. After backup completion the database writes a message containing the complete path of the backup piece and the device type to the alert log.

The control file autobackup filename has a default format of %F for all device types, so that the RMAN can guess the file location and restore the controlfile without a repository. All autobackup formats must include the %F variable.

The format %F translates into c-IIIIIIIIII-YYYYMMDD-QQ, where
IIIIIIIIII - stands for DBID.
YYYYMMDD - Time stamp of the day the backup is generated
QQ is the hex sequence starts with 00 and has a maximum of FF

Use the following command to configure the Control file Autobackup format
RMAN> CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/oradata/cf _spfile_%F';

Use following command to write to an Automatic Storage Management disk group
RMAN> CONFIGURE CONTROLFILE AUTOBACKUP FOR DEVICE TYPE DISK TO '+DGROUP1/%F';

Use the following commands to clear control file autobackup formats for a device:
RMAN>CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK CLEAR;
RMAN>CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE sbt CLEAR;

You can use SET CONTROLFILE AUTOBACKUP FORMAT command to override the configured autobackup format at session level
RMAN> SET CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '/backup/cf_spfile_%F';
RMAN> BACKUP DATABASE;

If you have configured control file autobackup, you do not need a recovery catalog or target database control file to restore the control file in case if you lost all your control files.

Use the below command to restore the control file autobackup.
RMAN> RESTORE CONTROLFILE FROM AUTOBACKUP;

Regards
Satishbabu Gunukula
http://www.oracleracexpert.com