When you enable block change tracking in Oracle 11g, Oracle tracks the physical location of all database changes for incremental backups. RMAN automatically uses the change tracking file to determine which blocks need to be read during an incremental backup, and directly accesses those blocks to back them up. When block change tracking is not enabled, the entire datafile is read during each incremental backup to find and back up only the changed blocks, even if just a very small part of that datafile has changed since the previous backup.
The change tracking file is a binary file and resides in the fast recovery area (FRA). This file should be located in the same directory as your database files. To determine if block change tracking is already enabled, issue the following query:
To enable block change tracking, execute the following command (the database can be mounted or open):
The above command assumes you are using OMF, which will name the block change tracking file under the DB_CREATE_FILE_DEST location. If not using OMF, name the block change tracking file yourself: