Para-virtualization permits very high performance virtualization, even
on architectures like x86 that are traditionally very hard to
virtualize.
This approach requires operating systems to be ported to run on
Xen. Porting an OS to run on Xen is similar to supporting a new
hardware platform, however the process is simplified because the
para-virtual machine architecture is very similar to the underlying
native hardware. Even though operating system kernels must explicitly
support Xen, a key feature is that user space applications and
libraries do not require modification.
With hardware CPU virtualization as provided by Intel VT and AMD
Pacifica technology, the ability to run an unmodified guest OS kernel
is available. No porting of the OS is required, although some
additional driver support is necessary within Xen itself. Unlike
traditional full virtualization hypervisors, which suffer a tremendous
performance overhead, the combination of Xen and VT or Xen and
Pacifica technology complement one another to offer superb performance
for para-virtualized guest operating systems and full support for
unmodified guests running natively on the processor. Full support for
VT and Pacifica chipsets will appear in early 2006.
Paravirtualized Xen support is available for increasingly many
operating systems: currently, mature Linux support is available and
included in the standard distribution. Other OS ports--including
NetBSD, FreeBSD and Solaris x86 v10--are nearing completion.
