Can I install a 2nd Fusion drive on my 2012 Mac Mini?

I already bought the latest Mac Mini with the fusion drive before reading your notes on how I might install two hard drives.

I guess the 1st sub question is whether the fusion drive is physically larger than one regular hard drive. Too big and that would rule out installing a second drive.

My other computers are all two drive Raid 1 for safety in case one drive goes down. I have been doing this long enough to say that a dual disk Raid 1 really does protect my data.