
Xen has been fully integrated into Linux kernel 3.0 - valyala
http://blog.xen.org/index.php/2011/06/02/xen-celebrates-full-dom0-and-domu-support-in-linux-3-0/
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FooBarWidget
Can anybody tell me what's the matter with Xen? I believe that a few years ago
there was a lot of talking about Xen. Then all of that seemed to die out, and
it seemed that the kernel developers instead developed KVM because it's
simpler than Xen, and so the Xen developers had to re-release patches for
every kernel release. What's the current status of Xen? How widely is it used?
How widely is KVM used? Why is it being integrated into Linux now even though
KVM already exists?

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manvsmachine
Xen is still widely used. IIRC Xen provides the virtualization layer for AWS,
and it is used by some pretty large hosting providers (Linode comes to mind).
It also is packaged into a number of commercial commercial offerings. Oracle's
VM solution is really just Xen running on Red Hat with some optimizations for
their platform stack, same with Citrix. Clearly those two implementations
alone is going to be a decently-sized install base.

I don't know how much KVM is used in the wild, but it has been crowned the
"official" hypervisor for RHEL and Ubuntu, so I would guess that it it's been
steadily gaining steam w/ the OSS crowd.

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pwaring
KVM is used by Bytemark (www.bytemark.co.uk), who provide virtual machines for
hosting (smaller scale than Linode, mostly UK).

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evangineer
It's worth noting that Bytemark started out as and was for a very long time a
Xen shop.

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dgl
They started out with User Mode Linux actually, before Xen even existed.

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dasmoth
Indeed -- and stuck with it for quite some time. They were trialling Xen for
some time, but I don't think they ever deployed it on a terribly large scale.
Certainly, my VM went straight from UML to KVM.

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pwaring
I believe the management tools for Xen (or lack thereof) were the reason for
using KVM instead. None of my machines (I have 7 or 8) have ever used Xen.

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vivekl
Hats off to the Xen developers like Jeremy Fitzhardinge and others that
persevered despite what was quite stiff resistance from the Linux community
initially! Just to clarify, the major stumbling block was the Dom0 - Xen's
privileged domain which has normally been a fairly heavily customized Linux
kernel. A number of the DomU/guest components were already in the mainline for
a while. Then the core Dom0 components went in around 2.6.37. And now all the
PV backend drivers etc. are now in as well, paving the way for a vanilla Linux
kernel to be a fully functional dom0 under Xen.

Having watched the back-and-forth between the Xen and Linux community over
this inclusion business a bit, I feel the delay has actually been worth it in
hindsight. Linux's pvops abstraction is clean and impartial. With this Linux
has support for at least 3 virtualization technologies out of the box: KVM,
Xen, and lguest. Also, a lot of the jagged edges in the Xen dom0 patches have
been smoothed in this process.

This is also great news for private and public Xen-based deployments as well
as companies such as Oracle, Suse and others that built their own
virtualization platforms on top of Xen. Trying to get supported, well-tested
drivers for new hardware working with Xen has often been a major pain point
and required significant engineering resources. This was a major reason why
Ubuntu switched to KVM officially (Red Hat led the charge here but that was
mostly because they bought Qumranet - the company that built KVM). With this
Xen is significantly more maintainable and I expect to see at least some of
the distros to re-include xen as a virtualization option fairly soon!

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nphase
I wonder how this will play out on Red Hat now that Xen's been cut from RHEL6
(in favor of KVM)?

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wmf
Red Hat used to not care about Xen, and now they still don't care. But as long
as they don't deliberately break it, I guess RHEL 7 will inherit Xen support
for free from upstream Linux.

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rwmj
[Not speaking on behalf of Red Hat]

Even in RHEL 6 we have support for RHEL as a Xen guest.

However as aliguori says above, "Xen in Linux" is a misnomer: Xen is a
separate and completely different kernel (the "Xen hypervisor") and it seems
unlikely we'll be shipping that any time soon. No one gets rich by providing
paid support for two completely different and incompatible kernels.

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timbowhite
This is awesome news. Setting up a separate xen kernel for the host domain was
always a pain in the butt.

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tszming
Rackspace Cloud Servers and of coz Slicehost are also based on Xen.

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dualboot
Slicehost uses XenSource.

Rackspace uses XenServer which is not quite the same thing.

Rackspace is migrating all slicehost customers to their XenServer based
services and doing away with their XenSource product.

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lsc
XenServer and the xen.org stuff are very similar from the perspective of a
guest. I mean, administering them is a little different, but not that
different. there is rather a lot of shared code between the two systems;
Xen.org generally gets newer features first, and xenserver has for-pay
support.

Recently (well, I guess not that recently) the 'xl' command line from
xenserver was given back to xen.org. it's a lot nicer than 'xm' I think.

