I have just wasted several hours of my life trying to install OMV from a USB to a USB.
The symptom: every time the install stage got to creating the partition/filesystem, it would error out saying it couldn't create it. Tried different USB sticks. Was able to install from a USB stick to an actual USB HD, but never to another USB stick.
Was using 3.0.94. Finally as a last resort, I tried 3.0.86 and the install worked perfectly.
My conclusion? Something not right about 3.0.94. Don't know if it's a problem with the installer, or my old hardware, but it definitely doesn't work with my setup (which has been running the latest version of OMV for several years). I've always upgraded OMV through the web interface until recently when my USB stick shot craps and I had to reinstall OMV.