Webtest, I think administrollaattori is trying to hint at a better way of doing builds and testing ISO images. Virtualizing your build environment gives you more flexibility and control of the build environment, allows you pause, save, and clone machine states, and helps to prevent doing harm to your production OS environment. Virtualbox, vmware, Xen all have free versions that run in Windows, Linux, OS/X, and I think even BSD. Consider moving your build environment to a virtual machine instead of a USB drive. The virtual environment is also a great way to test new images. It allows you to try to boot the image without having to copy images to USB or having to reboot your system and go through POST.