I have a 3.06 GHz Intel Core 2 Duo with 4 GB ram, 500 GB internal drive (with over 200 GB free), running OS X 10.8.3. I have two 2 GB Seagate drives connected externally. After I turn on the external drives, a short time later the iMac slows to a crawl (pinwheels). I can't even get the drives to be ejected, as the pinwheel continues non-stop. I am forced to unplug the drives, which could corrupt my data, in order to get the iMac to run again. Once the external drives are disconnected, the iMac runs fine. WHY?
