What is a snapshot of a controlfile?

The snapshot controlfile is a copy of the controlfile that RMAN utilizes during long-running operations (such as backup). RMAN needs a read-consistent view of the controlfile for the backup operation, but by its nature the controlfile is extremely volatile. Instead of putting a lock on the controlfile and causing all kinds of database enqueue problems,RMAN makes a copy of the cfile called the snapshot controlfile, and uses itinstead of the actual controlfile. The snapshot is refreshed at the beginning of every backup. 

Configure snapshot controlfile name to '/proj/11/backup/snapf_prod11.f';

On Windows, the default location is ORACLE_HOME/database, and the default name of the snapshot control file is of the form SNCF<database name>.ORA. On Unix the default directory is $ORACLE_HOME/dbs, and the default name is snapcf_<database name>.f.

Enjoy:-)