Citrix: Cloud to carry Xen against VMware

In part one of our two-part interview, Citrix senior executive Ian Pratt explains how the company is looking to Xen's foothold in cloud computing to mount a challenge to virtualisation leader VMware

Citrix aims to beat VMware at virtualisation. A year ago it bought XenSource, the company created by the founders of the Xen open-source hypervisor, and switched the Citrix business focus to virtualisation.


Ian Pratt, the original project leader of Xen and a founder of XenSource, remains a Fellow of King's College, Cambridge, but is now also vice president for special products at Citrix — and remains chairman of

ZDNet UK spent a day at Citrix's UK headquarters with Pratt and his colleague, Simon Crosby, who has moved from chief technology officer of XenSource to become chief technology officer of Citrix. After lengthy briefings on Citrix products and the future of virtualisation, we sat down with Pratt to understand where Citrix is going and why.

In the first of what will be a two-part interview, Pratt discusses how Citrix hopes to make headway in the virtualisation market.

Q: At the moment there is a lot of publicity for VMware and Microsoft Hyper-V. Is there a danger XenWare will be overlooked — especially as it is difficult to measure market share in virtualisation? Could XenWare become the Liberal Democrats of virtualisation?
A: In the market, there is obviously a big incumbent player, VMware, and Microsoft has a very basic product that covers the low end. And then there is XenServer, which is going head to head with VMware, with an enterprise feature set.

If you look towards the cloud, all the cloud vendors use Xen. It gets used in all the largest deployments, by folks like Amazon and other large providers, because of all the features it offers.

It is very hard to judge what the market share is. With VMware, you just look at VMware's bank account.

But if you are looking at market share for Xen in general, you've got XenServer, Virtual Iron, XenApps and products from other companies. And then there are all the Linux distributions that include Xen, most of which are free, and no-one really has any idea of how many copies are in use.

Even with something like XenServer, because there's a free version, we keep stumbling into customers — particularly people doing software as a service, where it all runs on XenServer Express Edition [the free unsupported version of XenServer].

They haven't paid us any money as yet and they have thousands of servers running it. But we'd much rather they were running our stuff than VMware, because it's an opportunity for us.

With the Cloud Edition we recently announced, there will be lots of people wanting to pay for support and get features added.

If cloud providers are mostly on the free XenServer, is this the whole reason for the Cloud Edition — to turn them into 'real' customers and start getting some money in?
Simon Crosby has this analogy, that Xen is an engine and needs a car built around it. [The point of the analogy is that the Xen hypervisor is open source, with a GPL licence, so users can make additional technology outside that hypervisor and keep it proprietary, building commercial products that work with Xen].

If you are a cloud provider or a big software-as-a-service [SaaS] vendor, you can download the open-source engine and build your own car around it. That's fine if you have the engineering resource to do that, but a lot of this stuff is going to become...

...more commoditised. SaaS vendors don't all have very particular needs. They don't have to do this for themselves — they have just had to do it that way until now.

Cloud Edition gives them a standard framework, so they can just concentrate on the value-added bits that they are interested in.

So it's just like many software developments in the past, where it's become obvious that everyone is doing the same thing, and a supported version of that is produced?
Yes. And they just switch over to the supported version.

So VMware is the big competitor, then. What is the state of things between you and VMware at the moment?
VMware has been really successful as a virtualisation vendor. But virtualisation as a category will disappear. The basic use of virtualisation — server consolidation — is now a commodity.

Virtualisation will be included in every operating system and on every server. XenSource Express is built into every HP and Dell server, on a USB stick soldered into the box. Users can run multiple virtual machines on those machines out of the box.

This is the only thing VMware does, and it has 100,000 customers. VMware is preparing for this to happen, by building management tools. But this puts them in direct competition with huge established players, like Tivoli and HP OpenView.

Citrix's approach is to concentrate on application delivery. The function of an IT department is to deliver applications, and we are doing it end to end: from the datacentre to the client device.

We don't need to do systems management, and we don't need to compete head on. It is all about application delivery. People won't buy virtualisation — but they will buy high availability and fault tolerance.

Citrix has 200,000 customers. That's a pretty good beachhead to deliver more Citrix stuff to customers.

What is distinctively better about Xen's approach compared with VMware's?
We don't want to create a class of people called virtualisation administrators who you need to manage your virtual machines. That's how VMware works.

VMware is operating system virtualisation — or hardware virtualisation. That puts a lot of effort into a problem that is no longer there [since modern hardware from Intel and AMD has evolved to support virtualisation].

What we did was to start out with the idea that hardware should support virtualisation and the virtual machine should be aware. We call that paravirtualisation, and Microsoft calls it enlightenment. That's marketing.

If you employ virtualisation to get a separation not just in the hardware layer, then you can compose things dynamically. That's the way to bring down the real cost of IT.

We want to be as much of an appliance as possible. We've always seen Xen as an appliance that hosts virtual appliances. You want it to be an appliance and manage it like an appliance. It's like a Netgear router — you just plug it in and go. Adding a new machine to a XenServer pool should be as easy as that.

It is also quite hard to establish the relative performance of VMware's hypervisor and XenServer because of VMware's licensing terms. Are you working on a way round that problem?
The VMware EULA [end-user licensing agreement] prohibits the publication of any benchmark results to a third party. We tried to publish results in 2002, and that clause has been in the VMware EULA ever since.

As XenSource, we might have had fun and games around the policy, but as Citrix, we have to be more circumspect. It's possible to publish comparisons against 'Hypervisor A' and 'Hypervisor B', though.

How about comparisons with Microsoft? Pretty soon, Microsoft will be able to claim that all the people who have Server 2008 have Hyper-V, won't it?
Yes, but then there will be the question of how many people are using it, and how many people have the bits. If we wanted to measure Xen market share like that, we would be in great shape, because every Linux distro has Xen included in it.