Well I have a 24" imac, 250gb HD. my HD is filling up quick with design projects and itunes. I currently have a 250gb ext. HD for my time machine backup. I don't really want to install a new higher capacity HD internally so I thought about putting my itunes and design projects on another ext but figured it would run slow? I figured the internal hd would cause me to loose everything, or i may be wrong. Any ideas on my situation?