So I've had this problem before, never solved it, large files on my drives (mostly videos) can't seem to be defragged no matter what I do, In the screenshot you will notice that i selected a single file "a good day to die hard" and tried to defrag it individually and it just starts and boom "this operation cannot be done" any ideas? as this is not a very fast pc Intel Pentium Dual Core E6700 @ 3.85GHz you do tend to notice the sluggishness when those files are heavily fragmented.