I think more my question was, how does it know whether to record on the usb drive or the MAC. Or do I need to unplug the USB?

I have a HDFX-4K. Currently have a USB hard drive attached. Been having some difficulties with playback. I read that I could use a MAC for storage. So I downloaded and installed the software.

First problem, I wanted to change storage location. Couldn't get that to work so postpone that till later ...