I do know that my MVIII uses a hack of a lot less
power booting
off a remote disk than it did spinning up 3 MFM drives. I can only
assume that the RAxx use even more juice.
Dunno about anything as new as an RA9x, but the RA81 draws 30A surge
current (which is why they have that daisy-chain power sequencer
port), and 8A steady-state. That's a big honkin' motor in there, plus
several square feet of controllers.
I'd recommend RA7x instead. The RA9x drives are 8", while the RA7x
drives are 5.25".