While I do use external USB hard drives for backup purposes, I use an external StarTech docking station that holds 2 SSD drives (see
).
I find the SSD drives are VERY fast. I use the first one for all things X-Plane... the 2nd is a back-up of the first. I make a backup copy of the X-Plane drive often... but only if everything ran without glitches, or if I added planes/scenery, etc.
HTH