How to import assets without getting readonly fatal error

Using an external hard drive to run Unity 5.1

Right now I am attempting to do a simple 2d platformer tutorial, and when I attempted to import standard assets to the project, it tries to decompress and Unity crashes with the error:
‘Fatal Error: attempt to write a readonly database’ → Quit

How can I solve that error, especially since I rely on the external hard drive to run and save projects with Unity?

I opted to move the project to internal storage, but CNET has some info on solving read-only for external hard drives, which may help if you are set on using an external drive.