Many of us have tried ways to run multiple operating systems on a single physical computer. Probably the most notable product in this areahas beenVMWare . Microsoft is catching on withits ownVirtual PC offering and of course there is Parallels which came out of the Apple world.
One thing about virtualization that is not widely known is that it is an old principle (in computer time terms). It was actually used in the days when mainframes were the only game in town for high end computing needs.
One problem that was often encountered when running multiple operating systems on the same physical computer is that of performance. There was always a significant degradation which largely speaking ruled out any chance of using virtualization in a production server setting. I first noticed changes in this whilst with a client in Arizona back in 2005. They had built a very flexible lab-QA-Test environment using VMWare. This interested me because they were able to load-test code fairly aggressively and get reasonable performance even though it was running in a virtual environment, that got me thinking.
Recently, I attended a conference in San Antonio Texas and there was a presentation by a company called Xensource. Xensource seem to be taking virtualization to a new level and I think I am right in saying the company came out of an open-source initiative called “xen”.Xensource were recently acquired by Citrix and I think this in indicative of another trend centered around creating distributable complete environmentswith runnable applications. This is addressed to a certain extent by this section from the Xensource web site.
- Portability: The use of abstract devices within virtual machines, combined with the encapsulation of virtual data in file-backed or volume-backed virtual disks, makes it easy to move virtual machines from one physical system to another, for maintenance, more effective resource utilization, or simply for replicated provisioning.In many cases, running virtual machines can even be moved while they are online, with no interruption to service.
We will be doing more work here at Alagad around the whole topic of virtualization.The next steps will be to take one of our Windows 2003 lab servers and install Xensource on there and then follow that by attempting to install different operating systems and hopefully ColdFusion. I will be blogging about that in the near future as we move through each stage.
It seems to us that virtualized servers will play a large part in the continuing evolution of computing. I wonder how many servers sitting in data centers and dedicated to a specific task are under utilized ?
DougHughes.net 
Comments on: "Server Virtualization – The Coming Wave" (3)
Hm, that’s nice but this is something VMWare has been doing for a good number of years – since the release of ESX 2.x. In fact, in their current server virtualization solution (ESX v3), you can let the host systems move the guests around automatically, dictated by resource requirements set for the guests, and the available resources on the hosts at any time. So if you’ve defined that your SQL server should have n IO available, and its current host has too much IO because of unexepected load on the fileserver, the hosts can automatically move it to another host with less load.
I think far too many do the mistake of judging the capabilities of VMWare by Workstation and Server, and fail to realize the power of the most mature and powerful server virtualization solution on the market: VMWare ESX. Sure, it costs a bit of money, but just the money you save on hardware support plans will make that up in a few months, max.
My understanding of the problem with Xen is that it was designed to run hosts that are specifically adapted to run within it, which means for example Windows and other closed source OSes are at a disadvantage. This might have changed tho…
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Tomas, thanks for your detailed response and in fairness you make some good points. From what I have seen so far Xensource are more Windows-centric and I think are focusing more on using virtualized environments for distributed applications, hence the particular interest of Citrix who bought them. Citrix are not known to be a networking or server powerhouse. You made me think of something with this post which I will investigate more carefully; thanks.
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No problems.
Hm… I’ll be interested to see what you find if you’ll be blogging it. My impression of Xen from hearing about it from some bsd enthusiast friends is the exact opposite of yours, partly reinforced by FAQ items 1.3 and 1.4 here: http://wiki.xensource.com/xenwiki/XenFaq#head-bb579ddda3999d87064a36b7d847fad8e39440ae
As for Windows-centric I should say we’re a pure Windows-shop. That is, all our servers except for 3 ESX hosts run Windows. We currently have about 18 virtual Windows 2003 servers running on two of the ESX boxes, the third runs 10 XP based VMs. I don’t really see the underlying OS of the virtualization platform as relevant, other than that it should be as lean and optimized for virtualization as possible. If you still want a Windows host platform, you really should look into Windows 2008 + Viridian too. I’ve been testing RC0 for a while, and it’s really way ahead of previous Virtual Servers from MS. It’s still a long way from ESX though.
In the application virtualization space, MS also has some interesting things built around the Softgrid stuff they bought with Softricity last year. I have looked at it more for client apps than server apps, so I don’t know how it scales etc but definately interesting.
If you’d like to hear some experiences with ESX feel free to contact me directly (I assume you can get my email address from the posting, if not let me know)
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