"Why should VMs be mounted on physical machines? Xen
uses a virtual hard drive (VHD). This virtual hard drive is stored
somewhere on the Xen-based host machine. For the purposes of this
tip, I will refer to this "somewhere" as the storage back end.
There are two common ways to configure the storage back end. The
easiest solution is to use a disk image file which is created in
the host operating system. This also is the location where the VM
installs its files. The alternative to this method is to use a
device as the storage back end. This can be a logical volume, a
partition or a logical unit number (LUN) on the storage area
network (SAN). Essentially you can use any storage device for this
purpose, and due to the performance benefits this solution is used
"By mounting a virtual machine in the host operating system
(OS), you can do all maintenance that you need to do rather easily.
If the virtual machine runs Linux as its operating system, this is
particularly easy because the Xen host OS is Linux as well. It also
helps that the most useful tools for VM maintenance in a Xen-based
environment are installed by default in the Linux host. But even if
the virtual machine uses Windows there are lots of options. You use
one of the many new technology file system (NTFS) maintenance tools
that are available nowadays."