[CoLoCo] XEN and QEMU

[Kevin Fries]

On Sun, 2008-06-08 at 21:17 -0400, Ringo Kamens wrote:
> I am currently running the most recent ubuntu on AMD64 and I want to
> run a virtual machine from within it using Xen or QEMU. I'm new to
> this field, so I have a few questions. I looked at the wikipedia
> entries for both of them but I don't exactly get how they are
> different. If I'm going to be running a 64-bit virtual machine on a
> 64-bit processor, is there any which will be inherently better? How
> about a 32-bit virtual machine on a 64-bit processor? Also, how does
> networking work for these, ie does it just route through an interface
> I configure on my host machine to forward traffic?
> Thanks for any help you can give me,

When it comes to virtualization, you essentially have four options:

1) QEMU/KVM - This is the grand daddy of virtualization.  It is an old
and mostly stable product that is not always going to be your fastest
option.  The biggest advantage of QEMU is that you can emulate different
CPU types.  Therefore, unlike any of the other options mentioned here,
you can emulate a PPC and run Mac OS/9 or emulate an ARM based
processor.  The KVM variety bypasses much of this cross platform for
x86, and runs kernel level optimizations.  In order for this to work,
your kernel must have VM support.  With either flavor, every VM will
look like just any other program to the underlying OS.

2) XEN - Xen is different from all the others in that it is what is
known as a hypervisor.  In this case, You have one core that all VMs can
share.  Then the OS in each of the VMs can operate in a stack above
that.  In this case, there is a blurring of the lines between the host
and guest operating systems.  While not a fair analogy, you could think
of the other VMs in this each having their own process, while Xen treats
them almost more like threads.  Much faster and more efficient... that
is when everything plays nice.  If the guest OS is Xen aware, all is
good, but when it is not, then you must resort to processor level
support to handle non-Xen aware operating systems, such as Windows.
Microsoft has been working hard with XenSource to get Windows to be Xen
aware, and Vista was supposed to be the first MS OS to be so... Like
everything other than Aero, it did not make it.  Lets hold out hope for
Windows 7 (8? maybe 9, lol)

There are also two other major players in the virtualization world you
did not mention.  The two above only work with Linux as a host, and
Windows is always a spotty proposition.  The remainder of this are not
open source, but are free to use, and have a strong commitment to the
Linux community.

3) VMWare - This is the 800lb gorilla when you are talking virtual
machines.  This product just flat works.  Guaranteed, you can have a
server set up in minutes rather than hours or days.  If I had to pick an
annoyance on VMWare, it is that the driver needs to be recompiled every
time you upgrade your kernel.  It takes just a minute to do, but I
really wish it would happen automatically (KVM also has this issue if
the driver is not distributed in binary form).  The greatest advantage
to this product is that you will be able to find much more support for
this, than any other product, including both David and I on this list,
we are both heavy users of VMWare.  If your project has the posibility
of going commercial or large scale, this is probably your only real
choice.  The commercial packages have some serious feature sets that are
unmatched.  This is my choice for servers running multiple VMs to
provide services to end users.

4) VirtualBox - This is an excellent product with some great unique
features.  It is owned by Sun Microsystems, and is used in Solaris 10 as
their underlying VM engine... so you know this thing is rock solid.
There are three versions of this product: OSE; the limited free version;
and the commercial version.  The OSE is far too feature restricted for
me to advise.  As for the commercial version, I think you would be
better off with VMWare.  But the free non-FOSS version is terific!  In
my opinion the best of the bunch, and the one I use for my day to day
use (I run a VM on demand of Windows XP that when started blends in with
my Ubuntu desktop, and provides a popup start bar for Windows Start
menu).  This is my choice for running on desktop machines... Seamless
mode is worth the free admission alone.

In addition their is one new comer to the party:

5) Parallells - This product has been available to Mac users for some
time.  It has been very popular their.  Recently they have ported to
Windows, then to Linux.  I have no experience with this program, so can
neither endorse or advise against it.

I hope this rundown will help you make a well informed decision that
will help you accomplish your goals.

-- 
Kevin Fries
Senior Linux Engineer
Computer and Communications Technology, Inc
A Division of Japan Communications Inc.