How to enable block change tracking for faster incremental backups:

From Oracle 10g and onwards, you can enable block change tracking to speed up incremental backups. In short,

"if change tracking is enabled, RMAN uses the change tracking file to identify changed blocks for incremental backup, thus avoiding the need to scan every block in the datafile"

Syntax:

SQL> ALTER DATABASE ENABLE BLOCK CHANGE TRACKING USING FILE '/path/PRODDB_rman_change_track.dbf' REUSE;

Database altered.

More info here