Yeaaaaaaaaaaa. I'm not sure what the deal is. It shouldn't be a compatibility issue with any of the hardware I have in this machine.
Supermicro X10 board, I've tried the install with my HBA unplugged. i've tried different USB drives... just doesn't make sense.
No issues writing the installation files on any combination of hardware, EXCEPT a Supermicro board (X9DBL-iF) with a USB Flash drive as the installation target. For that, I get the exact same error message as you. I've tried this with multiple flash drives on both the internal USB "A" and on the back I/O, always the same "failed to partition..." error.
I haven't tried OMV3.x on it, but was able to install 4.1.3 onto an SSD.
Working with computers since the days when unboxing and set-up required 3 weeks with a soldering iron!