Episode: 12
Title: HPR0012: Xen
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0012/hpr0012.mp3
Transcribed: 2025-10-07 10:17:44

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Hello and welcome to Hacker Public Radio.
My name is Miro Vinci and I'll be your host today.
Previously in episodes of Today with a Techie, I discussed using VMware and virtualization
as a potential solution to different problems or to different test networks such as that
as you might need.
I believe I listed the example of a virtual cluster that I had built completely inside
of VMware.
I had a master node to slave nodes and all of the networking necessary to actually run
to actually test the cluster and it saved me bundles in terms of hardware because I only
needed one machine with one piece of software, you know, I'll be at VMware.
But this past semester, I took a class at the university, simply titled virtualization
and we spent the entire semester going through different journal articles and discussing
the technology of virtualization, a lot of the theory behind virtualization and a lot
of a lot of very interesting stuff and we concluded the semester with individual projects.
And so I hope to over the next few episodes that I have with Hacker Public Radio to explore
some of the things that we discussed in class and even potentially hopefully share my
project with you, with the community because it's a simple project, it was something that
I whipped together in the application that I'll actually be talking about here shortly and
has a potential, I feel to be a real benefit and hopefully in the coming months, I will
be able to talk about that some more coming weeks rather.
So today I wanted to discuss more and depthly of virtualization solution known as Zinn.
Now Zinn is spelled X-E-N and actually started with a professional article, a journal article
that came out in 2003 called Zinn and the Art of Virtualization, you know, and the main
authors on that were Paul Barham, Boris Dragovic and Kair Fraser and I would definitely
encourage you to go on the internet and you can go to websites like site seer at C-I-T-E-S-E-E-R.
You have to Google that or just use Google or Google Scholar to actually find this article.
It's 40 pages long and it really is an introduction, a good introduction to Zinn and how Zinn
works as a virtualization system or virtualization solution.
Some of you might be wondering what exactly is a virtualization software or virtualization
system to start with VMware as an example.
VMware will allow you to install their software onto your current operating system and then
install what they refer to as guest operating systems inside of that program.
Ultimately though what is going on is that guest operating system is installing completely
within software, installing completely within software to where it has no direct access
to any physical hardware because to the guest operating system, it has a complete set
of physical hardware which is completely being emulated by VMware.
Yes it is possible inside of say VMware workstation or VMware server to allow the guest
operating system to have access directly to pieces of hardware whether that is a CD-ROM
drive, USB hubs or USB devices, network cards, network interface devices.
You can allow that sort of access but by default and by its overall operation it is trying
to contain the guest operating system completely within emulated hardware or virtual hardware.
So now if you think about it, if you try and run just let's say a CD player application
within your guest operating system but you want to play it on the physical or you want to
play the physical CD-ROM drive, the CD player application has to send its you know system calls
and hardware calls and all that stuff through the guest operating system which gets down
to the virtual hardware which then VMware interprets those requests and then allows it
allows from that software application to take those hardware calls and hardware requests
down through the real operating system which is the operating system that lies beneath
the VMware, not above it, but beneath the VMware that allows then access to the physical
hardware.
So we've now added multiple layers that system calls and things like that have to get
through before they get to now comparing Zen to this virtualization model or virtualization
example, Zen is actually rather different.
Now for VMware Workstation and VMware Server it is a guest operating system installed
of a piece of software that was installed on top of a real operating system.
Now with Zen the guest operating system is installed onto what is referred to as a hypervisor.
Now the hypervisor is technically a piece of the Zen software that translates or handles
the system calls between the guest operating system and the hardware.
Now so this basically removes a lot of those layers between you know the software operating
system or software operating system, virtualization software, the true operating system down
to the real hardware and allows for a more direct access to the hardware.
Now even though a guest operating system has this more direct access access to hardware
is still controlled by Zen.
So just like in the VMware example if you want to allow a piece of hardware to have direct
access to a guest OS you can certainly do that and conversely if you don't want the
guest OS to have direct access or any access whatsoever to a piece of hardware you have
the ability to block that access and to deny access to that hardware or to that hardware
device.
If you were if you're following or if you get a chance to download the papers in the
virtualization figure one is a better description of you know of the Zen hypervisor and how
it fits into I guess the operating system model I don't know I don't this has a technical
term that I'm not familiar with but you'll see what's going on here.
Now to control the actual hypervisor as you'll see in this picture is and as you read in
this paper is something referred to as domain zero.
Within the Zen software guest operating systems are referred to as domains and all of all
of these things installing guest operating systems starting and stopping guest operating
systems as well as setting up hardware for guest operating systems or domains is all
controlled by domain zero and domain zero is a you know is a is a Linux is basically I mean
it it's Linux that has access to the Zen hypervisor and that allows these controls.
Okay so now we're aware of two different virtualizing solutions that are currently on the
market what's you know why would you choose one over the other well the answer comes
down to performance and performance issues as well as you know what you're going to do
with it now in terms of performance the Zen you know appears to do very very well and if
you look in in the article there's a complete section of evaluation and testing and figure
three is is a it's a graph that shows shows a benchmarks comparing native Linux so Linux
on a physical machine to what they call Zeno Linux which is their which is their Zen client
a VMware workstation but to be fair this is VMware workstation 3.2 and then user mode
Linux in all of these cases the Zeno Linux the Zen does almost as well as the native Linux
does or as the native hardware does and that's simply because it doesn't have the overhead of an
of an additional operating system operating underneath of Zen and underneath of what you know Zen
is trying to accomplish now to be fair though you can't really use this article to compare Zen
to VMware because in the article they use VMware workstation 3.2 and I don't know if it's
explained in this article or if it was in different articles that we read but you can go to and you
can go to the VMware website and you can find this in their in their in user license agreement
that you are not allowed to do benchmarking without VMware's express permission and I think in some
of their or in a recent change to their you know you know it's you you can you can do your own
benchmarks but they ask that you not publish the results and so even though they're up to like
VMware workstation 5.5 at the time this people was written VMware workstation 3.2
was the only version of VMware that VMware would license or allow them to do this benchmark on
and use the results in this article so you know so to to be fair to VMware I do want to point out
point out that difference and point out that thing but comparing Zen to native Linux so Linux
on a physical machine the numbers are incredible and that Zen performs very very well and so
they continued on with more benchmarks into let's see section 4.3 with running concurrent virtual
machines so they tested running running instances simultaneous instances of you know this benchmarking
program on you know Linux or native Linux and Zen and it's remarkable that looking in figure 4
and they're running what's called spec web 99 which was a a stress test of Apache servers or
a stress test for Apache servers and whenever there was one instance of the Apache server running
on Linux and Zen you know the native Linux did better than Zen did and it does that for the
two instances and for four instances but once we get to eight concurrent Apache servers that are
running the stress test analyzer now we get to a point where Zen actually performs better than
the native Linux does and I mean then that and that's because they're you know for each instance
of the Apache they're running it on different um different um domains and so you know so there's
not this conflicting overhead of software costs you know from from one instance to the other
azures with the native Linux or the you know the Linux on a physical machine and so Zen performs
very very well and you know if you read another pieces of literature depending on the application
that you're doing Zen runs incredibly well now again to be fair to VMware not that I by any way
I'm trying to um give plugs to VMware to encourage you to buy VMware's product or VMware products
they do have something called ESX server which is which is in in my opinion not that I've had direct
experience with it but appears to be very similar if not the same to this idea of pair of virtualization
now to completely you know reiterate that I don't want to give plugs to VMware because I mean
their products are commercial they cost and you know I am a free open source kind of guy I like
to support the open source community and Zen is actually an open source product now they do have a
apparent company or a the company the the people who created Zen you know created their own
company which was bought out by Citrix last year and so Zen does have a commercial solution
but they still have all of their source code online available for download for you know
absolutely free and I will definitely include a link in the show notes but that link is
Zen.org xen.org now you can go to ZenSource.org and that'll take you to the you know to the new
parent company Citrix but Zen.org xen.org is where you can get you can download it you can download
the user manual they have a wiki you know all sorts of that general open source communal
so that you can communicate that you can talk with others and that you can work with others
on your Zen project I'll also include a link in in a how to forge article that I use initially
when I got started with Zen and and if you just go to Zen or go to how to forge.com and you can
do a search for Zen devian it should be like the first link I used devian as my domain zero
to control my Zen and control the hypervisor it was able to install other devian domains or other
devian guest operating systems on my on my system on my Zen virtualized system I know there are
articles in the how to forge about how to install multiple versions of Linux or multiple flavors of
Linux onto our into a Zen environment including Ubuntu and Fedora core devian obviously etc so
definitely a worthwhile tool feel free also if you have any more questions you can email me directly
at MiroVinji at gmail.com that's m-i-r-o-v-e-n-g-i you can also find me in the
infinomicon channel on the free node irc server and in future episodes we'll be looking at more
virtualization technology that's come out especially some of the hardware technologies like the
vt enabled stuff I hope to discuss more theory about that about what goes into virtualization
and how some of these things like VMware like Zen work and and to potentially maybe look at
some of the more recent virtualization news which is like the VMVM escaping that many people
are working on you know looking at malware things like blue pill and just also how to really
use these technologies to your advantage and to you know what you're doing which you know gets
back to my class project that I hope to unveil at some point I hope that you've enjoyed today's
episode I'm again the MiroVinji and this has been hacker public radio thank you for listening
to hacker public radio hpr is sponsored by caro.net so head on over to caro.net for all your hosting