CHANGE BLOCK TRACKING (CBT)
Change Block Tracking or Change Tracking or CBT is making a record or journal of which blocks of a storage object were changed by I/O. A storage object is any logically contiguous space used for storage of data.
Now you need to keep in mind that CBT doesn’t keep track of what data was written, it only logs which areas of the object were written. Such track can be used for various applications, primarily for backup and restore. Usually such tracking is used to know what blocks have changed during a given time frame.