Examine your file collection: what's backed up; disk usage.
...However, Double File is project-based: it saves file checksums in directory listings you store locally. It facilitates planning and transitioning between computers and operating systems: snapshot your drive and safely archive it.
Listings can be searched when volumes are off site. Can read any volume mounted in Windows Explorer, including Linux and Mac volumes. Supports long path names.
SDifer is class library for backuping, synchronizing and snapshoting utility.
This is very simple framework for searching difference between a real folder and some its priviouse snapshot.
Utility can automaticly find and extract changes.