A brief history of Xen and XenSource

With the recent acquisition of XenSource by Citrix, it seems like a good idea to take a look at the history of Xen and XenSource so we have our bearings once the dust settles. This will be a brief look, but I'm sure more details will come out from you "Xen Experts" in the comments.

With the recent acquisition of XenSource by Citrix, it seems like a good idea to take a look at the history of Xen and XenSource so we have our bearings once the dust settles.  This will be a brief look, but I'm sure more details will come out from you "Xen Experts" in the comments.

First off, XenSource is a commercial company that sells a suite of enhancements and management products that augment an open-source hypervisor called Xen.  The lead developer for XenSource, Ian Pratt, is also the chief architect of the Xen open-source project - a competitive leg up by no small means.  In fact, XenSource is the key corporation behind the Xen hypervisor, so any enhancements to Xen also enhance XenSource (and anyone else who uses Xen, for that matter).

XenSource's goal, to put it unofficially, is to provide a solution akin to VMware, but using an open-source hypervisor.  This hypervisor has differences from VMware that some call advantages.  Some also call them disadvantages, which has led to what appears to be an epic battle akin to NT/Novell circa 1996.  More on this battle in future articles, I'm sure.  XenSource originally started as a pay-for support option for organizations that wanted to run the Xen hypervisor.  Over the last few years, they have created an impressive suite of management solutions for Xen, and have even collaborated with Microsoft.

Xen, first released to the public in 2003, uses a type of virtualization called "paravirtualization." This is essentially a software method of interfacing virtual machines to the host hardware...sort of an API.  Because of this, Linux operating systems have to have modifications made to run as a guest on a Xen server (called "Xen-enabled").  This is the part that sparked that battle between the VMware guys and the Xen guys.  VMware uses a method called Binary Translation, which uses hidden hardware instructions to accomplish the same thing (that is, functional virtual machines). 

With the advent of Intel VT and AMD SVM, Xen now supports Windows virtual machines without changes to the guest OS (Windows virtual machines were not supported prior to support for VT and SVM).  This has brought the virtualization methods of the two companies a little closer together, but still fundamentally different. 

Note: I tried really hard to get that right, but if I missed something or am way off base, please email me and let me know the real deal.

From 2003 to 2005, Xen's relative youth, it was developed into a popular desktop hypervisor.  Able to support only one 32-bit processor, there wasn't much enterprise appeal.  This is when XenSource was simply a commercial Xen support company.  In 2005, XenSource released Xen v3, the first enterprise-class release of Xen (even though it was called version 3, it was really the first).  With this release Xen could run on servers with up to 32 processors, and was the first version with built-in support for Intel's VT technology.  AMD hadn't released SVM yet, but it too was eventually supported.  In addition to the processor enhancements, Xen v3 also introduced support for Physical Address Extensions (PAE) to support 32-bit host servers with more than 4GB of memory.  At this point, Xen still only supported Xen-enabled Linux guest operating systems.

The v3 release of Xen also resulted in XenSource's first legitimate approach to an enterprise solution - XenOptimizer.  XenOptimizer was intended to be bridge the gap between Xen and VMware.  Remember, Xen is just the hypervisor, XenOptimizer from XenSource (confusing, eh?) was the management interface.  With XenOptimizer, admins were now able to manage multiple servers from a common interface for server provisioning and resource control. 

In late 2006, XenSource released its first version of XenEnterprise 3.0, a product meant to directly compete with VMware.  Based on v3.03 of Xen, it included an new management and monitoring console built on XenOptimizer and, most importantly, support for Windows guest operating systems.  This is largely the result of a July 2006 partnership agreement between XenSource and Microsoft to provide interoperability between XenSource and Microsoft's new hypervisor, codename Viridian.  Also resulting from this agreement, Xen-enabled Linux guests will be able to run on Viridian and XenEnterprise will be able to recognize Viridian's VHD (Virtual Hard Drive) files.

Flash forward to just over a week ago, when XenSource released XenEnterprise v4.  This is a landmark release for XenSource, and builds on the foundation laid by XenEnterprise v3.  The new version adds features and functionality that are meant to rival VMware, but at less than half the cost (list price, of course).  Among the new features are:

  • Integrated storage management software, Veritas Storage Foundation from Symantec
  • XenMotion, the Xen equivalent to VMware's VMotion
  • A new system management console, XenCenter, allowing administrators to manage virtual machines just as a user would do with VMware VirtualCenter.

XenEnterprise v4 runs on the latest version of Xen, v3.1 (sigh...Citrix, please change XenSource's name to something else...like Tazwell or Oddibe). 

That brings us up to the present day.  It’s been a busy (and profitable) last few weeks for XenSource, and Citrix is so light in the pocketbook now that they’ve had to tie themselves down with all the red tape they’ve gotten stuck in by purchasing the sponsor company of an open-sourced hypervisor.  It’s in Citrix’s best interest to continue to develop Xen, since any improvements will undoubtedly help them.  The crazy thing is that those same improvements will now also help out their new direct competitor – VirtualIron. 

Some quick thoughts about the future…

As the dust has settled over the past few days and I’ve had a chance to look at the reactions of many people, both analysts and admins, it’s pretty clear that the nobody knows for sure what is going to come of all this.  There are obvious correlations between XenEnterprise and Citrix Desktop Server, and Citrix may even be able to use some of the Xen technology to enhance AIE and Citrix Streaming server.  So far, the most interesting thing I’ve heard comes from a guest’s post in our forums.  An excerpt from that post reads:

“It seems to me that Citrix is looking to strike the same deal with Microsoft regarding virtualization that it has regarding Terminal Services: Microsoft provides the underlying infrastructure and Citrix provides the enterprise solution on top of it. If this is true, then this purchase was probably done with Microsoft’s blessing, and positions Microsoft and Citrix as partners against VMware.”

If that is indeed the case, then the next year or so could be pretty cool in a UFC/Rugby/Australian Rules Football kind of way.

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Dear XXX,

As you are by now aware, Citrix announced its intention to acquire Xen-based virtualization provider, XenSource, for $500MM. I wanted to take this opportunity to address VMware’s valued partner community and provide our position on this acquisition.

First, I want to thank-you for your continued investment in VMware. We all have a tremendous market opportunity in front of us with a huge potential for VMware partners and I look forward to working with you to achieve it. Together we have already achieved great success, with 20,000 customers adopting VMware virtualization solutions, but we are all just getting started!

Regarding the new Citrix/XenSource combination, while we will always encourage you to sell the solutions that best meet customer requirements, we are also confident that VMware solutions are a superior offering. This acquisition should have no impact on VMware’s market position. As VMware has the expertise and the technology to enable unparalleled customer success today, customers will continue to demand VMware solutions.

One thing I do want to make clear is that VMware will continue to fully support those customers that have chosen to deploy both VMware and Citrix solutions. While we acknowledge that VMware and Citrix will now compete for some new accounts, current joint VMware/Citrix customers will see no change in VMware support.

VMware’s commitment to you, our partners, is that we will continue to build superior virtualization solutions, we will continue to innovate, and we will continue to work with our channel partners to enable the success of all our shared customers. All of you, our world-class partners, are very important to us, and we at VMware will commit to doing everything possible to ensure that your investment in us and our shared future will be greatly rewarded.

VMware Analysis

VMware Offers a Superior Solution

The following points articulate why VMware is the best virtual infrastructure partner and solution provider.

1. Pioneer, Leader, Innovator - VMware pioneered x86 virtualization and has established a record of technology innovation and proven customer success.

XenSource failed to gain measurable market share. Its upcoming XenEnterprise v4 release still has major shortcomings compared to VMware Infrastructure 3.

Citrix provides impressive technology, but its competencies and resources are not in the field of system-level virtualization, which is what XenSource needs in order to deliver an enterprise virtualization solution. VMware has an unmatched infrastructure in place to develop, certify and test virtualization solutions. We continue to invest massively to extend our R&D and support.

In spite of recent acquisitions, Citrix revenues and energies are still heavily focused on Presentation Server. Citrix corporate and field organizations will need time to develop the expertise required to support partners and customers with unfamiliar virtualization products.

2. Complete x86 Server Virtual Infrastructure Today - VMware provides a complete, proven virtualization solution that allows an organization to expand beyond server consolidation. VMware customers can leverage technologies such as seamless VMotion, DRS, HA, DR, and VCB to obtain complete benefits of an agile, secure datacenter.

XenSource still cannot deliver the capabilities of 3rd-generation VMware virtual infrastructure. Citrix technology will


Virtual Iron has had LiveMotion and other VMware-like features for much longer that XenSource.  Compared to Virtual Iron's features, XenSource's are pretty untested and immature.  Virtual Iron is also credited with a lot of the improvements made to the Xen hypervisor; they are one of the most active contributors to the Xen project.

XenSource has less than $1M in revenues.  The $5M that's been floating around is really $1M + $4M.  The $4M was a one-time fee collected from Microsoft for the Xen/Viridian interoperability project.


Have read this:  http://www.crn.com/software/201400070?pgno=1

VI is a solid product, but very complicated to get up and running.  In short they all do the same thing, it is just who does it better.  "

Compared to Virtual Iron's features, XenSource's are pretty untested and immature."

Do you have facts? 

Who in VMware managed to send out such stupid email? This only proves how unprofessional and immature the VMware organization is. Don’t they have PR-advisors to help them out…
I'm surprised to hear you say that.  It's actually the easiest of all to install.  Each virtualization server PXE-boots its from bare metal.  You don't have to install ANYTHING on the VI server.  We found it to be extremely easy and efficient to set up and get up and running.

Yes, I do have facts.  As of last March, they had absolutely nothing to speak of, while VI has been supporting these advanced management features for over a year.  Meanwhile, VMware has been watching VI like a hawk, silently acknowledging them to be the only viable direct threat.

Do you have facts to the contrary?


Anyone considered the fact that Citrix bought Xensource by mistake and is now looking through articles and forums to find the best use for their newly purchased company? :-)

In all honesty i think the guest comment is the best suggestion i have heard so far, and i think we have all heard alot. But it would make sense as Microsoft ventures into uncharted territory that they would want one of they strong alliance partners with them. And to spice it up, i am pretty sure that Microsoft would have had their hands full legal-wise if they had tried to purchase Xensource(like another BM.Com reader commented). So this works out for all of us i think.. We need virtualization of OS, Apps, Phones, Pizzas and whatnot to spice up our Centralization and consolidation Toolbox.. and now we might get solutions from the vendors we already do business with... Provided ofcourse that Microsoft finishes up Viridian and delivers a decent product :-)



I don't think Citrix would shell out $500M by mistake...I'm sure that whatever their reason is, they had the price tag justified long ago.  Granted, to us, it's hard to find enough uses for XenSource to make up $500M dollars, especially in the short-term, but I'm optimistic that they have a plan in place already.

By the way, we're working on the font thing.  Should have it fixed site-wide soon.
Got it

I think it's interesting that they picked XenSource when SWSoft or VI would have been a better choice.   For $500+ million dollars they could have had access to a hypervisor AND OS Virtualization (Virtuozzo).

From a "Let's spend money" page,  how about we petition Citrix to dump some money into building up Presentation Server.  Sure 4.5 came out recently that made a few improvements over 4.0, but lets be honest, it's nothing more than a feature pack at best.  How about adding some real functionality like "Session Virtualization", the ability to Migrate Session to another servers.  Application Templates,  Server templates, ability to filter applications via policy, ability to take a server offline and still be able to adminster it via  RDP AND ICA, ability to publish apps via policies,  EVEN the ability to add a NEW server to a group of published applications (with out having to open each app, use a script, or use a 3rd party product),  and may finish the CMC to AMC conversion.



Sounds like a lot to ask from a 7 year old architecture.

Washington had to cross the Delaware, Citrix will get past it too. <para-phrase>


Seems to me that Citrix may be looking at purchasing Virtual Iron to complete the set. After all, it's built on the same Xen platform. I'm sure they've got an extra one or two hundred million to make another purchase.


"I think it's interesting that they picked XenSource when SWSoft or VI would have been a better choice.   For $500+ million dollars they could have had access to a hypervisor AND OS Virtualization (Virtuozzo)."

It's not just about buying software/technology Joe, XenSource is UK/US based while SWSoft is Russian.

Diane Greene, VMWare's CEO. Good eh? :)

That is very true.  Even Cisco has been know to aquire companies because they are in the general area of their corporate offices.



But at the same time,  $500 million dollars is a lot of money to pay for location and a handfull of employees.  I'm sure it will all work out.


Perhaps, but some of the requests are not difficult to implements.  We wrote our own gui to publish multiple apps to a server and that only took a day or so and I'll bet that feature is in the top ten most requested.
But why accept $100 -200 million when Citrix just raised the bar to $500-$600 million and if you're VI you're thinking your version is better.
Carl Eschenbach
Executive Vice President
Worldwide Field and Sales Operations

Maybe they wanted into this field and this is the only one who would sell.

Don't put to much credit into Citrix, there a big 'C' now. 

VI would have been a better buy but either they were not selling or asked for a lot of $$$s. 

SWsoft is based in US from what i can see - Washington DC