Belkin XM Commander Manuale Utente Scaricare il pdf (Pagina 9)

Chapter 1

Introduction

Xen is a paravirtualising virtual machine monitor (VMM), or ‘hypervisor’, for the x86

processor architecture. Xen can securely execute multiple virtual machines on a single

physical system with close-to-native performance. The virtual machine technology

facilitates enterprise-grade functionality, including:

• Virtual machines with performance close to native hardware.

• Live migration of running virtual machines between physical hosts.

• Excellent hardware support (supports most Linux device drivers).

• Sandboxed, restartable device drivers.

Paravirtualisation permits very high performance virtualisation, even on architectures

like x86 that are traditionally very hard to virtualise. The drawback of this approach

is that it 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 sim-

pliﬁed because the paravirtual 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.

Xen support is available for increasingly many operating systems: right now, Linux

2.4, Linux 2.6 and NetBSD are available for Xen 2.0. A FreeBSD port is undergoing

testing and will be incorporated into the release soon. Other OS ports, including Plan

9, are in progress. We hope that that arch-xen patches will be incorporated into the

mainstream releases of these operating systems in due course (as has already happened

for NetBSD).

Possible usage scenarios for Xen include:

Kernel development. Test and debug kernel modiﬁcations in a sandboxed virtual ma-

chine — no need for a separate test machine.

Multiple OS conﬁgurations. Run multiple operating systems simultaneously, for in-

stance for compatibility or QA purposes.

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Belkin XM Commander Manuale Utente Pagina 9