Yes, you can open a Photo library on any volume. However, Apple places a restriction on what non-Apple photo apps can do — non-Apple photo apps can only open the “System Photo Library”. You can tell if this library is the system library by looking in Photos Preferences. If you would like to learn more about multiple libraries and RAW Power, here is a video: https://www.youtube.com/watch?v=nR0wRXPg7Tw&list=PLgF1Bfd-tVLa8sizMIG2g42x6CdPUmHsb&index=8