For ?automated testing purposes, we need to use removable USB mass storage devices, e.g. to test USB-only features such as the USB installer or persistence.

On a headless test server in a datacenter, one does not want to rely on a set of physical USB sticks being plugged in.

Therefore, these USB mass storage devices must be emulated in software, and should probably use files as underlying storage.



  • obsoleted by g-mass-storage
  • not in Debian kernel as of 3.2.21-3


Works fine with qemu-kvm (1.0+dfsg-11) and libvirt (0.9.12-3):

modprobe dummy-hcd is_high_speed=1
modprobe g_mass_storage file=/tmp/test.usb removable=1

Then I use qemu-kvm + libvirt USB 2.0 passthrough to lend that virtual USB mass storage device to a qemu-kvm VM, which I boot from a Tails 0.12 ISO, that I clone onto the virtual USB device using the Tails USB installer.

Then I unplug the virtual CD drive, and boot the same VM from the virtual USB mass storage device, onto which I successfully setup a Tails persistent volume. Rebooting, enabling the persistent volume does work.


  • Not in Debian kernel as of 3.2.21-3, asked in Debian bug #678731
  • All underlying files must be listed at module load time; this should not be a problem, but still a limitation to be kept in mind.


qemu (1.1.0+dfsg-1) and qemu-kvm (1.0+dfsg-11) know how to emulate a USB mass storage device, using -usbdevice (deprecated) or (roughly) a combination of -drive file=path_to_test_file.usb,if=none and -device usb-storage,drive=DRIVE-ID. At least with qemu-kvm:

  • one can boot from such a USB device
  • virt-manager (0.9.1-4) and libvirt (0.9.12-3) allow to add and configure such a device, and plug it into a virtual USB 2.0 controller


  • removable property: by default the emulated USB disk is not marked as removable; qemu and qemu-kvm from Wheezy support emulating removable USB devices, but libvirt has no way to pass this option.