GPD-G7 can read NTFS without problem.
how did you formated your hard drive?
in another hand, G7 have CIFS support. plug your HDD on your PC, share as a lan resource and connect with CIFS Manager.
with this, you can access to your hard drive, via WIFI.
for more examples, i suggest to you to read this article (in spanish, use translator):http://manguiro.blogspot.com.es/2013/07/cifs-directorybind-sambadroid-cifs.html
I'm using this in my G7 to mount android folder, and now i get installed so many games on it. Of course, i can?t play these games away from my lan, but for my testings and current usage of this device, is enough for me.
if you check my G7 videos, all of them than put "CIFS" in their name, means that i?m loading via CIFS, using this method. https://www.youtube.com/playlist?list=PLXPqQ3mj-_IcgE_NPL8pRWuJm6CMws0u4