I wanted to install some software on to an OS which was installed on a USB flash drive, so I created a virtual machine that booted up of the USB drive.

I found it needed root permissions, and it is probably a good idea to un-mount the device before hand.

VBoxManage internalcommands createrawvmdk -filename ./HardDisks/USB-test.vmdk -rawdisk /dev/sdd

Once you’ve done this, you then need to set this new virtual hard drive as a virtual machines hard drive.

This might work with booting from hard drives e.g dual boot.
Good luck.