hello there. i've been experiencing this problem for some time now. whenever i'm copying files from hard drive to another, and if the HDD the windows is on, is at 100% usage the pc becomes sluggish as hell.
right now i'm patching total war rome 2... in the task manager i can see the hard drive at 100% usage, the CPU at 6-20% usage.... and the whole system is very slow. UPDATE... is done now and the system is fast again.
No its just using all the hard drive can give and so there is little performance left for normal operation since it sounds like it is doing a lot of writing and reading when you updated total war.