I set up the RMAN backup for the company I am working. One thing I always try to figure out is why the incremental backups takes more time than the full backup. I do a full backup on Sunday and do an incremental level 1 backup everyday. But the incremental backup takes 2 hours while the full backup only takes about 1 hour. Today I figured out a way.
Login with sqlplus as sysadba,
alter database enable block change tracking using file '$ORACLE_BASE/admin/bct/bct.dbf';
Then guess what, the incremental backups starts takeing 8 minutes!