I have a 3TB drive as a separate data drive on Windows 8.1 This drive contains an old installation of windows 7. The drive size reported in disk management is as expected 2794.39GB. the Properties window shows that 2.5TB has been used and 231 GB is free for a total capacity of 2.72GB. The problem is that I cannot figure out why it is showing 2.5TB used. Unfortunately I did not pay attention to the growth rate and do not know when this occurred. It may have been when i was still running that drive as my primary OS drive with Windows 7, or it may have occurred since adding it as a secondary drive to my Windows 8.1 system.
I've granted myself access to the System Volume Information folder and recycle bin so those folders are accounted for.
I've used WinDirStat and TreeSize so see where the space is being used up both report a total of 1.2TB in use. So i should have roughtly another 1.5TB of free space left that is unaccounted for.