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Re: [Xen-users] Is Xen really a Type 1 Hypervisor?



On 11/20/2012 10:03 PM, quadibloc wrote:
While Xen is indeed actually a Type 1 hypervisor, confusion is
understandable.

With VMware ESXi, another Type 1 hypervisor, you install ESXi on a machine
using an ESXi install disk. And then ESXi runs on that machine, hosting
whatever guest operating systems you install on it. You manage the
hypervisor over the network from another machine, which may be running
Windows, running the vSphere Client.

VMware used to make a Type 2 hypervisor called VMware GSX Server, which ran
on top of a server operating system, and which could therefore be managed
from the keyboard and screen of the server itself.

When you install Xen, though, you use a Linux install disk. After you have
installed Linux, you add a Xen package which both puts Xen administration
tools in the copy of Linux you have installed, and installs Xen itself as
another operating system. Then you use GRUB to switch things around so that
Xen boots up, but it still subsequently starts that copy of Linux as a
special guest operating system with the power to administer Xen.

So it's a Type 1 hypervisor that does a good job of appearing like a Type 2
hypervisor if you don't pay attention to what's going on technically behind
the scenes. You install Linux, then you boot into the Linux that you
installed to control the hypervisor - just as you would have if it were Type
2.

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Hi quadibloc,
Xen definitely is type1 hypervisor. You have to differentiate between Xen hypervisor and dom0 management domain. In VMware ESX you have both hypervisor and management stack in one 'package', but in Xen it's not. Xen has separate small-size hypervisor running directly on top of HW and dom0 is started just on top of it. dom0 is communicating via special communication channels with Xen hypervisor and providing only management stack. Therefore the dom0 kernel needs to be patched to support this communication channels and it could be GNU/Linux or NetBSD or any other system you would like to patch to support Xen management. Xen's advantage of ESX is that it doesn't need to 'support' the HW it is running on. The HW needs to be supported only by dom0.

For better understanding read this: http://wiki.xen.org/wiki/Xen_Overview and continue with http://wiki.xen.org/wiki/Xen_Beginners_Guide .

Best regards,
--
Peter Viskup

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