Copying files to and from external hard drives usually hangs part way through the copy process, especially when I use a USB hub and copy between external drives or memory sticks. The same process works fine on my tower running Windows 7. I've tried numerous solutions found on the internet and nothing seems to help. A common answer is that the Surface Pro 4 doesn't supply enough power via the USB port so I bought a powered USB hub but that didn't solve the problem. Another common suggestion is to turn off write caching but that didn't help either. Any assistance would be greatly appreciated. Thanks.