I just ordered an KingWin Three bay hardrive rack, part number KF-3001-BK (this is a SATA drive device) which is installed in a computer tower case. I ordered it from www.Amazon.com
It requires removing the top two hardrives from the case. After the rack is installed the drives are placed in one of the bays and close the cover.This device allows for installing 3 drives in the space used by 2 drives in a tower case The drives can be hot swaped by opening the cover and a lever pushes the drive out from the rear.
You can use this system to change operating systems or clone (backup)the sysyem drive. If it fails, shut down swap system drives, startup the computer and your back in operation.
There is also a 4 bay unit, part number KF-4001-bk which takes up all the drive space in the tower case.