In-Depth

Citrix Aims High

Known for application virtualization, the company shook the hypervisor market with the strength of a sonic boom when it bought open source maker XenSource.

When most in IT think of virtualization, turning a single server or PC into multiple machines immediately springs to mind. But there's an older style of virtualization pioneered by Citrix Systems Inc.: application streaming, or desktop virtualization. Here a server acts as multiple PCs and serves or streams the desktop environment to a remote machine, often a dumb terminal or low-end PC. Citrix Presentation Server, now known as XenApp, is the gold standard for this style of computing. In fact, technology licensed from Citrix still drives Microsoft's own Windows Terminal Services, and has for a dozen years.

Building on its application virtualization success, Citrix took a huge leap into the very center of virtual computing when it bought XenSource, an open source company, for a half billion dollars this past October. With XenSource (re-named XenServer) now in hand, Citrix has two styles of server virtualization. Its first approach, according to Greg Shields, Virtualization Review columnist and author of the e-book The Shortcut Guide to Selecting the Right Virtualization Solution (Realtime Publishers, 2007), is called "paravirtualization." Here, the hardware is not emulated as it is with the hardware virtualization approach offered by VMware Inc. and Microsoft. Instead, the operating system is modified by writing to specific APIs that allow for the hosting of virtual machines (VMs), Shields explains. While paravirtualization can be faster than hardware virtualization, it's dependent on the OS makers porting their OSes.

Citrix/Xen also now supports what's typically called hardware virtualization, where the hypervisor runs on top of an unmodified host OS. This allows XenServer to support a broader range of OSes, including Windows Server. And now the company's moving to directly support virtualization-ready processors from Intel Corp. and Advanced Micro Devices Inc.

"Hardware assist is very important in our architecture and it's important in the Microsoft architecture. Hardware assist is here to stay," says Peter Levine, Citrix senior vice president and general manager for the Virtualization and Management Division, and former head of XenSource. Levine argues that the Xen approach is more efficient than VMware's. "The Xen hypervisor is a very lightweight infrastructure compared to what ESX has, just because of the design points and the assumption that there would be hardware assist under the covers." Just as XenServer has two approaches to virtualization, the company now has two approaches to desktop virtualization, or thin-client computing. The incumbent solution is XenApp. But after buying XenSource, Citrix built another solution.

"XenDesktop is a new product that sends Windows images out to a virtual desktop. It uses some Presentation Server concepts, but it's not the same product," explains Levine. XenDesktop combines elements of the previous Citrix Desktop, such as the ICA protocol that also powers Presentation Server, with the Xen hypervisor.

Competition for the desktop is heating up. VMware is also moving into the application virtualization space with its acquisition of Thinstall. While this isn't the same as desktop virtualization, the end result is nearly the same -- the application comes off of a server and is accessed by a remote PC or thin client.

Building Value
While Citrix has a complete virtualization platform, it's not overly religious about pushing its own platform. In fact, Citrix is more than happy to support its own and Microsoft's hypervisors. "I always expect us to have two product areas based on two different hypervisors," explains Levine. The main goal for Citrix is building value on top of the core virtualization infrastructure.

"We're about building a virtualization platform that can run without any OS agenda. So we'll run a bare-metal virtualization. In the case of Microsoft, where there's more of an OS agenda, some folks may want to first adopt the Microsoft platform and then build services on top of that. In other cases, others may want to build bare-metal virtualization and then build services on top of that. There will be a class of customer who wants the latest and greatest virtualization features, in which case we'll be able to offer those on top of Xen, obviously much more easily than on top of something [else]," Levine says. So what exactly are those add-ons?"There are a lot of virtualization services that we add on top of the engine. Examples would be the high availability, resource pooling or the notion of clustering of physical machines, [or] the notion of motion, i. e. moving guests from one physical node to another. Resource management is another," adds Levine.

The 451 Group backs Citrix's market analysis. According to a recent report by analyst Rachel Chalmers, "the hypervisor -- the software layer that enables physical machines to run multiple virtual machines -- has become a commodity." The real action will be in the layer above, which 451 calls "management." Some typical management functions are part of this definition, such as administration, optimization and managing. But 451 also includes some non-traditional items, such as backup and high availability, security and test labs. So who will define the platform of the future?"I think a big part of the not-too-distant future is making the platform a property of the hardware itself. If a company is blessed enough to have the virtualization platform completed with the hardware at the time of purchase, that simplifies the entire user experience. The platform-enhanced part of the hardware will start to drive what the accepted platforms will be out there in the market," says Levine.

If all goes well, the core platform may not even matter. "One of the good things about our relationship with Microsoft is we're committed to offering interoperability between Xen and Viridian [now called Hyper-V]. We're going to be very closely aligned with Viridian APIs and Xen APIs and make them more similar than not," Levine points out. In January, Citrix and Microsoft formalized this relationship, with Citrix promising to ensure that XenSource and Hyper-V are interoperable. In a deal similar to the Terminal Services agreement 18 years ago, the companies also agreed to co-market virtualization tools, and make sure that Microsoft System Center can manage Citrix software.

More Information

Q&A: Citrix CEO Pushes Xen, Aligns with Microsoft
By Doug Barney and Keith Ward

Citrix Systems Inc. CEO Mark Templeton leads a software company with sales of more than $1 billion per year, and was instrumental in the acquisition of the XenSource hypervisor. XenServer, with the sales and marketing might of Citrix behind it, is poised to become one of the biggest players in virtualization. Virtualization Review Editor in Chief Doug Barney and Editor Keith Ward talked with Templeton about the XenSource purchase and his company's strategy in the virtualization space.

Why did Citrix buy XenSource?
They were the only viable virtual infrastructure company to buy, actually. We felt strongly that we needed to own the core technology underlying the value that's on top of this open source hypervisor. The rationale is pretty simple: We had this idea that we'd need to be able to control the core platform in virtualization from the desktop all the way to the data center, in order to deliver on the value proposition that we've been promising customers around the kind of security, performance, flexibility and cost model [as well as] an end-to-end strategy for delivering apps.

It became obvious to us that virtual infrastructure was a core technology for us; we needed to be able to really bake it into our products for application delivery, and owning it was important. When we looked in the marketplace, though there were a few options, XenSource was by far the logical option for us to take.

Since the acquisition, XenSource is no longer a free product. Theres been some anger in the open source community that it's now a proprietary product. Some have even claimed it's a betrayal of the ideals of the free open source software community. Is that a legitimate complaint?
No, I think it's not. All complaints are legitimate, but it's a question of what the facts are. The facts here are really straightforward. Everything that was free before the acquisition -- specifically the Xen open source hypervisor -- [is still free]. We have re-branded [it] as the XenServer Express. And by the way, [the free hypervisor is] better than [it was] before. So, they're still free and they're better.

What do you see as the state of third-party development in the virtualization market right now?
It's pretty rich. It's an area where venture firms are looking at business plans and funding them when there's an experienced team and a great idea. There's money flowing to these ideas. Second, all of the platforms you can build on as virtualization ecosystem partners are maturing, especially when it comes to SDKs and APIs. That goes for all the key players: VMware, Citrix and Microsoft. The innovation platform is there for third parties.

And there are companies like Citrix and Microsoft in the marketplace that are trying to drive the growth of the marketplace -- that should raise all ships and require a large ecosystem of ISVs to add value to the core platforms. I think it's in a good place and growing very rapidly.

Over the next three to five years, how we think
about virtualization will be redefined.
-- Mark Templeton, Citrix
Mark Templeton, Citrix

One of your chief partners has always been Microsoft. Now Microsoft is becoming, perhaps, more of a competitor. Is Redmond your biggest competitor right now, along with your biggest partner?
No. We don't think of it and look at it like that at all. In fact, we think that our opportunity to partner with Microsoft on Hyper-V is identical to the partnership we built on top of Terminal Services.

Whether we're talking about server virtualization or desktop virtualization, we think that there's a massive opportunity to partner with Microsoft to build value-added products on top of Hyper-V. And by the way, everything that we're building on top of the Xen open source hypervisor will transfer in terms of our knowledge and a lot of the technology, etc., onto Hyper-V -- so we'll be able to give customers a choice [of] a bare-metal type implementation or a Hyper-V implementation.

Obviously, we have a huge customer base that is very Microsoft-centric, and we think that they'll naturally pick Hyper-V as the underlying virtualization infrastructure and put our value-added services on top, both for server and desktop virtualization.

Both Citrix and Microsoft, at least on the virtualization side, are looking up at VMware. What is it going to take to knock VMware off its perch and become the top dog?
I'll speak for Citrix. We're not trying to knock VMware off their perch. The virtualization market will naturally evolve over the next three to five years in a way that everyone is going to have to keep up. I think that the next-generation foundation is being laid right now on next-generation hypervisor technologies. Next-generation providers like Citrix are looking at virtualization in a more holistic way, and in two dimensions. First of all, not only at the server ... basically not only at the logic and data tier, but at the user tier and at the desktop tier and having the ability to orchestrate all of that end-to-end. Over the next three to five years, how we think about virtualization will be redefined. That redefinition will be the opportunity, then, to maybe re-stack players in some different ways.

One of the stumbling blocks to virtualization being adoption is a lack of standards in the industry. How do you see that developing?
It's a little bit early for standards to form -- to have formed. You're seeing the beginnings between VHD [Virtual Hard Disk] and OVS [Open Value Subscription] ... sort of the fundamentals. The hypercall API is an example of another area that we could see more standardization around how systems talk to virtual infrastructure. It's pretty early in the overall development of the marketplace. Remember, this year the estimate is only 9 percent of new servers shipped will receive virtualization software. It's hard for standards to develop when a market is so young and untapped.

With Microsoft entering, with our role in it, and then the growing role of Xen itself as it's embedded in products from Oracle and Red Hat and Novell and Sun, etc., there will be more and more reason for the industry to come together around standards. The logical one will be, let's get the machine into a format that, once it's built, can be moved among virtual infrastructure platforms.

Who's driving the adoption of virtualization technology?
It's being driven from the bottom up. This isn't a top-down kind of a marketplace. I don't see virtualization or virtual infrastructure appearing on any sort of CIO list as priorities [in the] top 10. The technology ... happens to be a low-level technology historically.

Exposing the intangible value of virtualization to the CIO, to the CEO, to the CFO, etc., is the single biggest thing that you can do to help enable growth. When we talk to IT organizations, here's what they tell us over and over and over again: "You need to come to our shop because we can't tell this story to the CEO and CFO, they won't listen to us ... they don't understand, they think that we're 'propeller heads' and we don't know how to speak the language."

Our biggest challenge as a company is to get those intangibles to be seen in a way where they have business value that can then be translated into an architecture for the future. That's an approach we're taking that's maybe a little different to what others are taking.

About the Author

Doug Barney is editor in chief of Redmond magazine and the VP, editorial director of Redmond Media Group.

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