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Re: [Xen-users] PCI/VGA passthrough: differences between Xen and ESXi?

  • To: xen-users@xxxxxxxxxxxxx
  • From: Alexandre Kouznetsov <alk@xxxxxxxxxx>
  • Date: Tue, 02 Apr 2013 11:18:11 -0600
  • Delivery-date: Tue, 02 Apr 2013 17:19:05 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>


A little correction, if I may.

El 02/04/13 10:54, David TECHER escribió:
dom0 = the main (first) hypervisor, hosting all virtual machines -- like
your Mac OS X
domU = any virtual machine.

Dom0 is not the hypervisor. The way Xen works, all OS's or machines running on the host are "Domains", and they run over a layer they call hypervisor. The hypervisor is a very low level piece of software between the actual OS's and the hardware.

The difference between Dom0 and the rest of DomUs is that Dom0 is "privileged": hypervisor accepts system calls from this virtual machine and allows it to access the hardware directly. Beside that, there is no much technical difference between Dom0 and DomU. The practice is to assign Dom0 very few resources dedicated and is used almost exclusively to control the hypervisor (start/stop VM's, etc.) and access to storage and networking. Anything actually useful the computer do is done within a DomU.

There are some restrictions about what OS may run on Dom0: It has to be paravirtualized, it has to run a kernel specifically supporting Dom0 operation, it need to have a toolkit to control the hypervisor (xe, xl or xm). Specifically this are the restrictions that would prevent to run a MacOS X, for example, on Dom0: Xen hypervisor would not understand it.


Alexandre Kouznetsov

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