Drobo

Drobo 5D default interface: TB or USB?

Anyone tried to connect both USB3 and Thunderbolt to two different devices at the same time? Wondering if only one interface will work or both.
In the dashboard we have the “Active interface” to monitor that.
My idea is: connect the Thunderbolt to a Mac and the USB to a NAS.
Ideally when the Mac is turned on I’d wish the Thunderbolt to take priority over the USB, and use the Drobo 5D with the Mac. When the Mac is turned off the USB connection should become active and Drobo be seen by the NAS.

Would it work? Or both interfaces will be active at the same time (causing a mess)? Or USB takes priority over Thunderbolt?