My two cents as i like to test omv in a virtual server while my new hardware is on the pipe ...
I you do an install for the last version 5.2.4 used the two package:
VirtualBox 5.2.4 platform packages
VirtualBox 5.2.4 Oracle VM VirtualBox Extension Pack
Start VBox for the first time and stop it.
Connect your USB stick to your Windows machine.
Press Windows Key + R, type diskmgmt.msc
search for your usb stick and remember the number allowed buy windows. --> #
open a Command Prompt as Administrator
CD's to your VirtualBox’s default installation directory
type VBoxManage internalcommands createrawvmdk -filename X:\the directorie of your choice\usb.vmdk -rawdisk \\.\PhysicalDrive# --> where X is your HDD drive letter and # your drive number.
This will create a vdk image link to your usb stick.
When creating your virtual machine, create the booting virtual hdd using the option "add existing disk" and point to X:\the directorie of your choice\usb.vmdk.
Done.
** warning ** Do not force a reboot by closing your virtualbox, this could screew your usb data, same for power outage !! **
