XenServer: Free and (almost) open source


The XenServer virtualization platform from Citrix Systems Inc., which became a free product in early 2009, is turning open source with the release of Xen Cloud Platform (XCP).

“The first versions of [XCP] are going out now, which is essentially the XenServer core platform being open sourced,” said Simon Crosby, CTO of Citrix.

Announced by the Citrix-hosted Xen.org community in late August, XCP’s non-proprietary approach allows providers to develop cloud services that will work with virtual machines (VMs) from multiple vendors.

A key focus is providing “easy interoperability between internal enterprise ‘private clouds’ and leading external cloud platforms.”

“Xen Cloud Platform offers ISVs and service providers a complete cloud infrastructure platform with a powerful management stack based on open, standards-based APIs, support for multi-tenancy, SLA guarantees and detailed metrics for consumption-based charging,” states Xen.org.


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The basis for XCP is XenServer.

As a contribution to XCP, all the core features of XenServer are open sourced, explained Crosby.

One area that is not open source is the XenCenter console, he noted. “There is no point in open sourcing it anyway because it’s a Windows .NET GUI and nobody cares about that,” he said.

The objective behind making XenServer open source, according to Crosby, was to “essentially allow people who would consume open source to build clouds to consume it in that way.”

“If you look at the very largest providers, folks of the Amazon, Yahoo variety, they don’t want to consume a proprietary product. They want full visibility of the source code so they can modify it and they reserve the right to go in and hack,” said Crosby. 

Having a common platform among all the Xen vendors also “gives us a broader commonality in terms of compatibility and commonality management interfaces,” said Crosby.  

“It raises the bar for all of us, gives us a jointly stronger platform with which to compete with various other platforms, is all good and motivates in favour of open sourcing more rather than less,” he said.

What Citrix builds on top with their Essentials platform is what is going to help the company in their revenue stream, noted Mark Bowker, senior analyst at Enterprise Strategy Group Inc.

“They are essentially giving what they are going to open source away for free already so there’s nothing lost there,” he said.

Bowker finds the Xen Cloud initiative “super-interesting and important, especially if they can incorporate virtual machines that were created using VMware, Microsoft or Citrix XenServer and be able to leverage them and run them on the Xen cloud.”

But service providers are the biggest market for XCP and the platform has “a long way to go” before proving itself in the enterprise, according to Bowker.

“I think with any of these cloud initiatives, whether it’s Xen cloud or even well-established, what I call public, clouds, a Google or an Amazon, still have a lot to prove inside of any enterprise type of organization,” he said.

Bowker doubts the release of XCP would have any affect on the adoption of XenServer 5.5.

“XenServer 5.5 will appeal to the existing XenServer client or customer base and any other people looking at server virtualization, which is a very different initiative inside any organization than a cloud initiative a lot of time,” he said.

XenServer is a “winning” product for budget-pressured enterprises, SMBs, XenApp users, greenfield data centres and mixed OS environments, according to Crosby.

Speaking to a group of press in Budapest last week, Crosby highlighted XenServer 5.5 as meeting “100 per cent of our requirements for enterprise production virtualization.”

Within the first two quarters of XenServer becoming a free product, 20 per cent of Fortune 500 companies adopted the virtualization platform, he pointed out. About 40 per cent of those who download the free stack put the Essential stack into trial, he said.

The platform is up to 70 per cent more efficient than competing virtualization platforms and sees 30 to 40 per cent more users per server than any other virtualization platform, Crosby pointed out.

XenServer provides everything enterprises need to build a private cloud for 30 per cent of the cost, according to Crosby. Because Citrix charges per server and not per CPU, as Moore’s law delivers more CPU per server, the cheaper it gets, he explained.

This is a fair point, according to Bowker.

“What you are seeing already is Intel building platforms that are two-processor and now they are going to build platforms that are four CPUs. VMware licensing is aligned per CPU. The fact that Citrix is aligned per server does give them some benefits when it comes to what I would call initial pricing considerations,” he said.

Cost will also play a factor inside organizations as they deploy more than one hypervisor, Bowker noted. “In some cases … we are seeing some people that have made significant VMware investments actually choosing to deploy additional hypervisors, whether that’s XenServer or Hyper-V or any of the others,” he said. 

But what ultimately matters to someone considering the XenServer platform, according to Bowker, is how it will grow with their virtualization goals and initiatives.

“I think features are important, but I think they also need to understand … how is it going to take me from text and dev to consolidation into more of a dynamic, self-service IT?” he said.

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