I have 3tb in exfat. I know why you ask but it works on both mac and pc. But its super unreliable and stopped working. Still works on pc but not mac. Repair does nothing. So I cloned the disk I forget what program in windows 8.1 to another internal. Then erased the external as mac (so its fresh now and recognizes) and then put both into mac. I have the dual sata dock for the internals. I then cloned the disk with carbon copy cloner. I know its mac only now but at least it reads and I can always grab later form a flash stick or something and transfer to PC if I need any files. But exfat was too unreliable and stopped working finally. Anyhow I double checked the files and folders. All are the same size. But it says 900 something gb available and 2tb used on my exfat. But my mac os x journaled says only 1.5tb used and 1.5tb free approximately. How can it be if both files are the same size that I have 1.5tb free on mac and less than 1tb on exfat. Is this a difference between the file systems. Both are the same size but one says 2tb used and one only 1.5tb used. How can this be?