You may be able to get what you want by querying the IDB
omnidbutil -info
This will produce output for the Media Management part, and the Catalog part of the IDB.
You will want to find a line that says Filenames, under the column Diskspace Usage
Catalog database space usage:
Space used by Diskspace usage Records used Records total
============================================================================
Sessions 192 111 224
Objects 160 233 496
Object versions 352 367 624
Positions 160 565 960
Filenames 30112 481673 482240
You can get similiar output from the command
omnirpt -report db_size -tab -log [destination filename]
The '-tab' will prevent fields from truncating, and will produce a file that can be imported into Excell
IN both cases, unprotected sessions are not counted
However, Data Protector is not really setup to do what you are looking for