External Harddrives going to sleep/idle..

As far as I can tell, there isn't an option on the airport to keep the hard drive from going to sleep. Does anyone know a decent external USB hard drive that can be used with the airport extreme that does not go to sleep or has a very fast wake up time? Or is there any other known workaround to keep the harddrive from going to sleep? The drive I have is really slow at waking up and is pretty annoying for some of the uses I have for it.