True, it's not possible to have two hdds actively running at the same time, but you can make a simple switch to disable power to one drive while the other is running. I have 2 250s in my box and use the Ind-bios switching between them. I use seperate config files located on each drive to distinguish between the two (boot blue for one, red for the other). It only takes a couple of seconds to reboot and switch drives so its all good.