Linux Virtulization Options (or to KVM or not to KVM?).

[Mick Timony-3]

I'm in the process of replacing a few older servers, and I think this
would be a good opportunity to take advantage of virtualization to save
on hardware and related costs. Both Red Hat and Ubuntu are moving to
using KVM for their virtualization choice. I'm leaning towards using
Ubuntu with KVM as a host for both Linux and Windows 2003 server guests.
My google-fu hasn't turned much information about the performance of
guests, nor many hints of large scale implementations.

Has anyone used KVM with both Linux and Windows guests and would like to
share their experiences or advise?

I'm interested in how stable KVM is, and how well guest OS's perform
under KVM. And if anyone has done any (or come across any) performance
comparisons between KVM and VMWare and any other virtualization
technologies?

Plus, how easy is it to use? I want to make sure that less-experienced
folk will be able to manage whatever I build with minimal intervention
from me.

Many Thanks! :)
Mick Timony

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[Dan Ritter-2]

On Thu, Jun 25, 2009 at 12:51:27AM -0400, Mick T wrote:

> I'm in the process of replacing a few older servers, and I think this
> would be a good opportunity to take advantage of virtualization to save
> on hardware and related costs. Both Red Hat and Ubuntu are moving to
> using KVM for their virtualization choice. I'm leaning towards using
> Ubuntu with KVM as a host for both Linux and Windows 2003 server guests.
> My google-fu hasn't turned much information about the performance of
> guests, nor many hints of large scale implementations.
>
> Has anyone used KVM with both Linux and Windows guests and would like to
> share their experiences or advise?
>
> I'm interested in how stable KVM is, and how well guest OS's perform
> under KVM. And if anyone has done any (or come across any) performance
> comparisons between KVM and VMWare and any other virtualization
> technologies?
>
> Plus, how easy is it to use? I want to make sure that less-experienced
> folk will be able to manage whatever I build with minimal intervention
> from me.

I have a bunch of Debian Etch/32 VMs running on Debian Lenny/64
hosts with KVM.

It's production-quality stable. Note that the stability of your
VM's kernel is important -- several tests with other distros did
not go well. I also found that emulating the e1000 NIC was much
better than anything else for this.

Using the Red Hat-developed libvirt tools is very simple, at
least on a par with VMWare's products. For more complex
scenarios, it's a good idea to read the man pages and make sure
you understand what you're doing.

-dsr-



--
http://tao.merseine.nu/~dsr/eula.html is hereby incorporated by reference.

You can't defend freedom by getting rid of it.
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[Jerry Feldman-2]

KVM is built into the kernel, so if you get an update, you don't have to
go to a vendor for an update. My experience is with the desktop, and I
had Windows XP, Windows Vista Ultimate, and Windows 7 running
simultaneous under KVM on Fedora 10. I also have Fedora 10 and Windows
XP running as guest OS's under Virtualbox on my laptop. My experience is
desktop, not server. There are some limitations, but you can do stuff
with a VM you can't do with real iron. (Years ago while converting
Burroughs to IBM we had 4 physical tape drives, and I had confirgured 16
virtual under VM/370. We had one job that under Burroughs only used 4
tapes at any one time, but would dynamically open several during the
run. With IBM (OS/VS1 you had to allocate all the drives during the
beginning of the job in JCL. So, what we did was simply use virtual tape
drives and assign and deassign them as necessary). Basically, you should
be able to accomplish wat you want under KVM. However, there are some
features that are not available from the GUI, but are from the command
line - QEMU.

BTW: Remember to enable the virtual flags on your processor.

On 06/25/2009 12:51 AM, Mick T wrote:

> I'm in the process of replacing a few older servers, and I think this
> would be a good opportunity to take advantage of virtualization to save
> on hardware and related costs. Both Red Hat and Ubuntu are moving to
> using KVM for their virtualization choice. I'm leaning towards using
> Ubuntu with KVM as a host for both Linux and Windows 2003 server guests.
> My google-fu hasn't turned much information about the performance of
> guests, nor many hints of large scale implementations.
>
> Has anyone used KVM with both Linux and Windows guests and would like to
> share their experiences or advise?
>
> I'm interested in how stable KVM is, and how well guest OS's perform
> under KVM. And if anyone has done any (or come across any) performance
> comparisons between KVM and VMWare and any other virtualization
> technologies?
>
> Plus, how easy is it to use? I want to make sure that less-experienced
> folk will be able to manage whatever I build with minimal intervention
> from me.
>
>  

--
Jerry Feldman <gaf@...>
Boston Linux and Unix
PGP key id: 537C5846
PGP Key fingerprint: 3D1B 8377 A3C0 A5F2 ECBB  CA3B 4607 4319 537C 5846



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[Kent Borg]

Mick T wrote :
> And if anyone has done any (or come across any) performance
> comparisons between KVM and VMWare and any other virtualization
> technologies?

For raw compute power, KVM is damn near as fast as running on raw hardware.

Last I looked IO performance is less for virtual machines. From what I
understand the Linux kernel and libraries are very well optimized for
speed, specifically: great effort has been made to not do any extra data
buffer copies. You know, pass pointers. Unfortunately virtual machines
need an extra data copy, both coming and going, and disk IO is fast
enough that a buffer copy is noticeable--depending on how you measure
it, disk access is half as fast as raw hardware. I think there are
efforts to avoid this, but it seems a tricky issue (I think the approach
is give the actual hardware to a guest--which means not being quite so
virtual anymore), and I don't think fixes for this are primetime yet.

I think lots of RAM is again your friend, disk caching always helps.
There also might be situations where a RAM disk makes sense and in that
case a RAM disk could be nearly as fast as raw hardware.

Obviously running virtual machines also wants to have lots of fast disk
space.


In a previous job I was planning on setting up two matched 1U machines
in a KVM-based configuration that would have been completely redundant
(doubly redundant in that each machine would have had mirrored SW raid 1
disks, redundant power supplies in each box, ECC RAM, etc.). The only
single-points-of-failure being: (1) a crossover cable between the two
boxes and the associated NICs, (2) the cabinet and larger facility where
the two machines would live, and (3) the common software and
administration. The design is capable of doing live migration of VMs
between machines, and therefore everything is effectively hot replaceable.

Unfortunately I never got the go-ahead to buy the ~$15K of hardware and
now I hear they have laid off everyone but a skeleton staff, I don't
know whether anyone is currently managing the decaying old hardware for
which they had no spares...


-kb

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