If after booting your vm, you realize that you forget to add a special block from dom0, it is still possible to add it when your vm are running. If you read the man page of xen : # man xm you will see that you need to do that : # xm block-attach our_domU_id phy:/dev/hda /dev/sda rw to add the real block device : /dev/hda from dom0 to a domU. But it doesn't work actually, and you will get this error : Error: Invalid mode Usage: xm block-attach Create a new virtual block device. Strange, as the mode in the man page did say : rw or ro # xm block-attach our_domU_id phy:/dev/hda /dev/sda w