Not sure why you think you can only use one drive (did I miss something)?
The Raspberry Pi B+, 2B and 3B(+) models all have 4 USB 2.0 ports, and as long as the drives are self powered I see no reason you could not have 4 drives. With a USB hub you should be able to use even more.
Do keep in mind that the Pi SoC only has a single USB 2.0 interface, so more drives would only be useful for more storage. If you were thinking of multiple drives for improved performance that would not be very effective.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?