Slow performance when copying files to and from USB devices

When I copy files to and from USB devices (camera, HDD, memory card) my system becomes very slow. For example if I want to close a window I move the mouse but it takes about 2 seconds or more before the mouse cursor moves. When I finally get the cursor over the x and click it nothing happens for 10+ seconds. I’ve tried this with all desktop effects disabled but the issue persists.