SSD, USB Memory Cards and MicroSD cards
I inserted a 256GB microSD card into the Gemini and apart from wanting to format it this was recognised and could be used. Inserting microSD cards into card readers and in the USB hubs repeatedly failed to see the card recognised {Android always wanted to format them first}. Not sure if this is an Android issue or not. In comparison memory cards were recognised fine. I tried a Samsung T3 SSD but again Android wanted to format it.
Literally just had this problem with my old Galaxy Note as well, so it's an Android issue. Android's just finicky about its SD cards.
Although in my case it led to a tangent of even worse issues.
I plugged a brand new 128GB card into it in order to transfer everything off the internal memory for putting on my Gemini. This card wasn't properly recognised by my desktop which couldn't recognise it as being any larger than 24GB when attempting to format it under Windows. Once inserted in the phone it told me the external SD card needed to be formatted in order to use it. Clicked ok, and it formatted the SD card correctly to 128GB.
And also formatted THE ENTIRE INTERNAL MEMORY OF THE PHONE which I guess is a "Feature" of Android 4.x which nobody decided to mention to users. Apparently it's not possible to format an external card without formatting the device's entire internal file structure too. Because reasons.
Ended up spending the next hour with it hooked up to my desktop via USB mass storage, running file recovery software to salvage 4GB of files off there...