O artigo Máquinas virtuais Linux não conseguem inicializar a partir do DVD no XenServer , embora para o XenServer 5.5 / 5,6, ainda possa pertencer aqui:
Unlike Microsoft Windows, which uses device drivers for paravirtualization, Linux virtual machines have a paravirtualized kernel. During the installation of Linux, it is actually running as a Hardware-Assisted Virtual Machine (HVM) and has access to DVD just like Windows. Once the Linux installation is complete, a Xen kernel is swapped in. However, as the paravirtualization is kernel based, this causes issues with accessing the DVD on boot, as the kernel is not loaded.
To allow the Linux virtual machine to boot from DVD, the virtual machine should be set to start in Recovery Mode, as shown in the following screen shot: