So I can under stand this; C: drive is main drive, you back it up to the D: drive. you don't use D: drive and want to turn it off. If I have this right, you backup to D: drive which you don't use anymore. If you backup the C: drive to the D: drive you in-fact use the D: drive. The only way to turn off/sleep additional HDD's is to remove them from the system. Your alternative is to setup a RAID of 0, 1, 5 or 10. Basically this will combine both drives in to one virtual drive and quit a common pratice these days.