Hi,
Currently, we use "Directory Sizer" (www.franzo.com/dirsizer2/) to track directory usage on our file servers.
It is like partition monitoring in OpManager but you can go down several level (configurable) of sub-folder through a web interface and see the evolution, so you can easily find where data has been added or deleted. This product isn't maintained anymore...
It would be nice to have a such feature in OpManager