Can't backup using both usbs at the same time

So I’m trying to create 2 different backups using 2 hard drives attached to both of the usb ports on the back of my ex2. But when I have both hard drives attached using the 2 usbs on the back of my ex2 it only shows one drive when I go to the backup settings. I’ve attached both drives to my computer and they showed up and I’ve used new cables and I’ve tried each drive in each port and no matter what I’ve tried it still only shows one drive. Am I missing a setting or something because I was under the impression when I bought it that I could use both usb drives at the same time.

I have no idea if this will apply to your situation, but I had the same problem, where one of the drives would appear and the other wouldn’t. I had formatted the drives as exFAT on a Mac using DiskUtility. The problem as I eventually traced it is that you have to format the DRIVE, not the VOLUME — formatting just the volume will result in an unrecognizable drive. I had done it correctly for one drive but not the other. Maybe that helps?