Add new virtual disk in XEN \"hot\
It is usual that after several years the space forecasts in a virtual machine are exceeded, in many cases because the project for which it has been destined is being a success and requires a larger storage size. What in principle may be a joy, also involves extra effort, since if the machine is in production, and we have more users, it means that we cannot turn off the machine for an hour to perform maintenance tasks. Thanks to XEN we can change the virtual hard disk without having excessive problems