If you just want an external drive, get an external drive. They're cheap.
If you need to be able to access multiple bare drives, the USB setup works (recommend a USB3 version), but there are internal SATA docks as well that can be set up for hot swapping, and fit into a 5.25" bay. I use one of those in my desktop, and it's a pretty decent setup that doesn't compromise stability or performance.
Canon 6D|24-105/4L IS USM|70-300/4-5.6 IS USM|40/2.8 STM|50/1.4 USM|85/1.8 USM|Samyang/Bower 14/2.8 Full-Manual Rectilinear Wide-angle|24/2.8 IS USM|
Canon EOS-M|11-22/4-5.6 IS STM|22/2 STM|EF-M 18-55/3.5-5.6 IS STM|