If you want to upgrade the "internal storage" the drive needs to be formatted by the shield and can not be used by anything else. It also limits this drive to 128GB, even if it holds more it only partitions off that quantity. For this storage a solid state flash drive is ideal. I use this Corsair. If you want to store your actual media as "external storage" there is no limit. I run my entire Plex server and use multiple WD Elements from 8-14TBs. I also have a few WD passports that are great because they don't take an external power source. To run multiple external hard drives directly from the shield I use a powered usb 3.0 hub. When I first started the journey I bricked 3 seagates in a month. I haven't had any issue with any of my WDs.