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Old 04-02-2011, 02:58 PM
Clint Byrum
 
Default Revisit Xen support

Excerpts from Serge van Ginderachter's message of Sat Apr 02 02:17:29 -0700 2011:
> On 2 April 2011 01:51, Clint Byrum <clint@ubuntu.com> wrote:
>
> > Other than people already having familiarity with Xen, what is a
> > compelling reason to support it in favor of, or in addition to, KVM?
> >
>
>
> Performance.
>

Serge, would you mind elaborating on that? I'm looking for facts.

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Old 04-02-2011, 02:59 PM
Clint Byrum
 
Default Revisit Xen support

Excerpts from Nathan Stratton Treadway's message of Sat Apr 02 04:14:19 -0700 2011:
> On Fri, Apr 01, 2011 at 16:51:04 -0700, Clint Byrum wrote:
> > Other than people already having familiarity with Xen, what is a
> > compelling reason to support it in favor of, or in addition to, KVM?
>
> I don't know all the details myself, but my coworkers did some testing
> and found that KVM was not able to isolate the virtual machines properly
> when there was a high IO load. In the end they switched back to
> running Debian on the Dom0 so we could use Xen.

Nathan, can you dig up any facts to back this up? I understand that you
weren't able to make KVM do what you knew how to do in Xen, but that
doesn't mean that KVM can't, just that the docs and interface are lacking.

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Old 04-02-2011, 03:03 PM
Clint Byrum
 
Default Revisit Xen support

Excerpts from Michael Zoet's message of Sat Apr 02 01:20:36 -0700 2011:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Am 02.04.2011 02:05, schrieb RaphaŽl Pinson:
> > On Sat, Apr 2, 2011 at 1:51 AM, Clint Byrum <clint@ubuntu.com> wrote:
> >> Excerpts from Chuck Short's message of Wed Mar 30 07:27:50 -0700 2011:
> >>
> >> Just playing devil's advocate here.
> >>
> >> Other than people already having familiarity with Xen, what is a
> >> compelling reason to support it in favor of, or in addition to, KVM?
> >
> >
> > Familiarity is a good reason I think, but also industry standards, and
> > hardware considerations. I think a lot of big companies expect major
> > distributions such as Ubuntu to provide a proper support for such a
> > standard as Xen. I know it came as a disappointment for us that using
> > Lucid as a (production) Xen dom0 was nearly impossible. Also, afair,
> > KVM requires hardware support. Most recent machines provide it, but
> > it's not rare to find servers that are too old to use it, and then
> > you'd rather use Xen for servers than VMWare...
> >
>
> I agree with that! Really big companies choose the things they know.
> And if they have to switch the distro they do it.
>

Noted. It sounds like Xen has a lot of inertia.

> Another advantage for Xen: it is more mature and easier to setup (at
> least for me because I have only one configuration file I can change
> with vim). Much more documentation around that works. You have much
> more network options. And you can easily assign a hardware NIC to a VM
> with Xen. With KVM this does not work on every hardware... (Now I have
> 2 15.000,- ? servers where I can not do the things with KVM I could
> easily do with Xen. This was a pitty experience...)
>

I feel like a broken record, but could you provide us with some facts
to back up these claims? Bug reports, manual pages, etc.


I feel like there is a lot of anecdotal evidence, but we shouldn't make
our decisions just because somebody says KVM can't do this or Xen can
do that.

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Old 04-02-2011, 03:26 PM
RaphaŽl Pinson
 
Default Revisit Xen support

On Sat, Apr 2, 2011 at 5:03 PM, Clint Byrum <clint@ubuntu.com> wrote:
> Noted. It sounds like Xen has a lot of inertia.

I'd say big companies have a lot of inertia. Once they have chosen to
invest in a technology, be it Xen or KVM, they build systems on this
technology for years, hire experts (and get their employees to become
experts), and they're not willing to reconsider their position a few
months after (or even years) after just because the trend has changed.
Xen was the state-of-the-art not so long ago, and it's already taken
these big companies long enough to use it. KVM is the medium-to-long
term future for many still.


> I feel like there is a lot of anecdotal evidence, but we shouldn't make
> our decisions just because somebody says KVM can't do this or Xen can
> do that.

I think many would agree that with current hardware and a brand new
DC, it's generally a better idea to invest in KVM than Xen. But if we
want Ubuntu to be an enterprise class OS for servers, that means we
need to provide the tools for people to be conservative if they want
to, and not to have to rethink the technology they've been
successfully using for years. So, encouring the use of KVM, I'm all
for it ; supporting the people who still need to use Xen and would
like to do so with Ubuntu, that's also a major point if you want
Ubuntu to be a reference in DCs.

Nowadays, who would use inetd to implement a network service if they
have xinetd at hand? I guess not many people. But we're not going to
remove inetd from Ubuntu, because a lot of old services still use it
and it's a standard per se, whether we use it for internal Ubuntu
development or not.


RaphaŽl

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Old 04-02-2011, 03:42 PM
Michael Zoet
 
Default Revisit Xen support

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Am 02.04.2011 17:03, schrieb Clint Byrum:

...

>> Another advantage for Xen: it is more mature and easier to setup (at
>> least for me because I have only one configuration file I can change
>> with vim). Much more documentation around that works. You have much
>> more network options. And you can easily assign a hardware NIC to a VM
>> with Xen. With KVM this does not work on every hardware... (Now I have
>> 2 15.000,- ? servers where I can not do the things with KVM I could
>> easily do with Xen. This was a pitty experience...)
>>
>
> I feel like a broken record, but could you provide us with some facts
> to back up these claims? Bug reports, manual pages, etc.

https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/741706

I am into further investigations here. But the two servers are already
in production use, so it is hard to test and get deeper into it. For
now I help myself with all kinds of proxying. But for real virtualized
gateways / routers there is no good solution for me now with KVM.

>
>
> I feel like there is a lot of anecdotal evidence, but we shouldn't make
> our decisions just because somebody says KVM can't do this or Xen can
> do that.
>

That's right but Unix/Linux SysAdmins need options to choose from! If
Xen integration is easily done then Ubuntu Server should provide these
option. If not SysAdmins are forced to use other distros like SLES or
CentOS. That's the trueth in many datacenters.

By the way: KVM has lot of advatages, too. As always you have to
choose which one fits best ;-).

Michael




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Old 04-02-2011, 04:23 PM
Serge van Ginderachter
 
Default Revisit Xen support

On 2 April 2011 16:58, Clint Byrum <clint@ubuntu.com> wrote:


> > Other than people already having familiarity with Xen, what is a

> > compelling reason to support it in favor of, or in addition to, KVM?

*
> Performance.

*Serge, would you mind elaborating on that? I'm looking for facts.


I tested several virtualisation technologies last year.*
I told my conclusions earlier on another list, but I'll copy paste them here for easier follow-up:


https://groups.google.com/d/msg/ganeti/JKejnQkAhgI/OdFBbww3K_cJ------------------------------------------------------------------------------------------------------------------------



About a small year ago, I have been conducting some various tests on
comparing different virtualisation technologies on different
platforms.


* tested VMWare ESXi, Xen on Debian and CentOS and KVM on Ubuntu and CentOS
* these tests have nothing to do with Ganeti, nor was there a test with DRBD,
* on Xen and KVM I tested using HVM/Virtio - not so on VMWare


* made different tests, stressing CPU, disk, memory and network on 1
till 10 concurrent vm's.
* client vm machines were all Debian Lenny


Some general conclusions were:
* VMWare ESXi was the clear winner,
* Xen on Debian Lenny was a close second, and the winner amongst Open


Source solutions.
* Xen performance is way better than KVM, especially when looking at disk access
* Xen performs in a more stable and predictable way, whilst KVM seemed
to perform more at random (which confirms Iustin's observations, )


* CentOS (5.4) performed remarkably well for being older sofwtare
versions (KVM, Xen, Linux kernel)
* performance on Ubuntu was really bad. The then recent Ubuntu Lucid
was far worse than CentOS 5.5 (both KVM)


* Disk speed on bare metal was 80MB/s
* on vm, those dropped to 40-20MB/s depending on the platform end
thenumber of concurrent access (= number of tested vm's)


Also, testing latency (lots of small writes): time dd if=/dev/zero
of=/dev/vda5 bs=512 count=100000 oflag=direct


* 4.6 MB/s on bare metal
* 728 KB/s on vm Ubuntu + KVM
* on vm Debian Lenny + Xen:don't have the number anymore but noted a
performance drop of only 20%

------------------------------------------------------------------------------------------------------------------------


It really struck me how Ubuntu's performance was really bad, even when comparing the then recent Lucid to a Red Hat backported kernel (still 2.6.18)


Of course, lots of things have evolved since then, but when looking at the major distro's, to update conclusions, one should look at Debian Squeeze and Red Hat 6.At least for Ubuntu, no things have changed if you only consider Ubuntu LTS as a contender (which is how I look at it at least).




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Old 04-02-2011, 04:47 PM
Chuck Short
 
Default Revisit Xen support

On Sat, 02 Apr 2011 08:03:11 -0700
Clint Byrum <clint@ubuntu.com> wrote:

> Excerpts from Michael Zoet's message of Sat Apr 02 01:20:36 -0700
> 2011:
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Am 02.04.2011 02:05, schrieb RaphaŽl Pinson:
> > > On Sat, Apr 2, 2011 at 1:51 AM, Clint Byrum <clint@ubuntu.com>
> > > wrote:
> > >> Excerpts from Chuck Short's message of Wed Mar 30 07:27:50 -0700
> > >> 2011:
> > >>
> > >> Just playing devil's advocate here.
> > >>
> > >> Other than people already having familiarity with Xen, what is a
> > >> compelling reason to support it in favor of, or in addition to,
> > >> KVM?
> > >
> > >
> > > Familiarity is a good reason I think, but also industry
> > > standards, and hardware considerations. I think a lot of big
> > > companies expect major distributions such as Ubuntu to provide a
> > > proper support for such a standard as Xen. I know it came as a
> > > disappointment for us that using Lucid as a (production) Xen dom0
> > > was nearly impossible. Also, afair, KVM requires hardware
> > > support. Most recent machines provide it, but it's not rare to
> > > find servers that are too old to use it, and then you'd rather
> > > use Xen for servers than VMWare...
> > >
> >
> > I agree with that! Really big companies choose the things they know.
> > And if they have to switch the distro they do it.
> >
>
> Noted. It sounds like Xen has a lot of inertia.
>
> > Another advantage for Xen: it is more mature and easier to setup (at
> > least for me because I have only one configuration file I can change
> > with vim). Much more documentation around that works. You have much
> > more network options. And you can easily assign a hardware NIC to a
> > VM with Xen. With KVM this does not work on every hardware... (Now
> > I have 2 15.000,- ? servers where I can not do the things with KVM
> > I could easily do with Xen. This was a pitty experience...)
> >
>
> I feel like a broken record, but could you provide us with some facts
> to back up these claims? Bug reports, manual pages, etc.
>
>

> I feel like there is a lot of anecdotal evidence, but we shouldn't
> make our decisions just because somebody says KVM can't do this or
> Xen can do that.
>

http://iopscience.iop.org/1742-6596/.../1742-6596_219_4_042005.pdf

Again Im not saying we should drop KVM in favor of XEN. if it something
our users want then. We should at least have a better solution in
Ubuntu than what we have now.

chuck

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Old 04-02-2011, 07:27 PM
Serge van Ginderachter
 
Default Revisit Xen support

On 2 April 2011 18:47, Chuck Short <chuck.short@canonical.com> wrote:


> I feel like there is a lot of anecdotal evidence, but we shouldn't

> make our decisions just because somebody says KVM can't do this or

> Xen can do that.
I fully agree with that.
Whilst I argument that Xen is definitely more performant than KVM, I'm mostly using KVM instead of Xen.So I never said KVM *was not good, definitley not.


Ubuntu needs to support both technologies, especially when Xen gets vanilla dom0 support.
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Old 04-03-2011, 06:15 AM
Clint Byrum
 
Default Revisit Xen support

Excerpts from Clint Byrum's message of Fri Apr 01 16:51:04 -0700 2011:
> Excerpts from Chuck Short's message of Wed Mar 30 07:27:50 -0700 2011:
> > Hi,
> >
> > In the past Xen support in Ubuntu as a host has been difficult for a
> > variety of reasons most notably no upstream kernel support. Now that
> > dom0 should be coming into the vanilla kernel soon. I think its time to
> > revisit supporting Xen as a hypervisor as well.
>
> Just playing devil's advocate here.
>
> Other than people already having familiarity with Xen, what is a
> compelling reason to support it in favor of, or in addition to, KVM?
>

Really awesome feedback guys, and thanks for putting up with my "tire
kicking" on this idea.

So what I'm reading is that KVM should be good once hardware catches
up with it. Xen takes advantage of older hardware more effectively,
and may also have a better I/O system.

Not one person has stood up and said that KVM blows Xen away, or is even
"better".

I have very little operational experience with either.. having had my
website and IMAP server on a Xen domU running CentOS 5 for a few years,
I can say that it is "fine" for the lightweight work of a wordpress blog
and courier-imap.

So, with all of that said, and xen dom0 support coming to the vanilla
kernel, it sounds like a slam dunk for Ubuntu to raise xen to first
class status.

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Old 04-03-2011, 01:28 PM
"Serge E. Hallyn"
 
Default Revisit Xen support

Quoting Serge van Ginderachter (serge@vanginderachter.be):
> On 2 April 2011 16:58, Clint Byrum <clint@ubuntu.com> wrote:

> Some general conclusions were:
>
> * VMWare ESXi was the clear winner,
> * Xen on Debian Lenny was a close second, and the winner amongst Open
> Source solutions.
> * Xen performance is way better than KVM, especially when looking at disk
> access
> * Xen performs in a more stable and predictable way, whilst KVM seemed
> to perform more at random (which confirms Iustin's observations, )
> * CentOS (5.4) performed remarkably well for being older sofwtare
> versions (KVM, Xen, Linux kernel)
> * performance on Ubuntu was really bad. The then recent Ubuntu Lucid
> was far worse than CentOS 5.5 (both KVM)

On the one hand, you can't make claims like this without giving
very detailed info on the storage configuration.

On the other hand, kvm (and libvirt) tend to make changes which impact
how you need to tune things to get best performance. Which is not
really acceptable in a real enterprise deployment.

We've gotten complaints before - valid IMHO - about 'undocumented
changes' like that. This is IMO a strong consideration for considering
re-enabling xen. It also may deserve a UDS topic on whethere there
is something we can do. Perhaps we can spend a week around alpha-3
time doing performance tests of various configurations. Perhaps we
can query the community for what they consider current best practices,
and document those at release time. Perhaps query, then do our week
of performance tests to validate, then document.

-serge
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