HD get hot, don't spin down.

I have 3 HD in a storage pool, and a single HD as the OS drive. The drives are Red Hot, and never spin down, this to despite the fact that they are set to be turned off after 20min of no use. What the heck, never had this issue in Win 7. I am concerned that this is going to kill my Hard Drives. I use this as a home sever so it stays on, but I am the only one who access it. So, there is no reason for the drives to be acting like they are.