I thought I had this fixed but apparently not.
I have my HD with Pi image for first usb port.
If I had a second usb drive in the first port, I have trouble moving if from windows back to Pi. I can see it through explorer in windows 10 under "media", I can create a folder. But I cannot add any files to the new folder or additional folders within. I get "access denied" within it making it useless.
Feels like it's an ownership/permission problem with windows but I'm not savy enough to fix it.