GigaOM Interview: Citrix CTO Simon Crosby on Xen, Microsoft & VMware


Virtualization underpins cloud computing by making it possible to separate the software from the hardware. So far the dominant player has been VMware, with about 95 percent of the market, but Simon Crosby, CTO of Citirix and former CTO of open source virtualization company XenSource (which Citrix acquired last year), plans to take that market back. The launch of Microsoft’s Hyper-V hypervisor is part of of his strategy. The rest revolves around services that “play nicely with others,” and free hypervisors embedded into servers and operating systems.

GigaOM: Can you tell me how the launch of Hyper-V affects Citrix Xen products?

Crosby: Our key founding philosophy was fast, free, compatible and ubiquitous hypervisors. Microsoft’s Hyper-V which is compatible with XenServer, is alright when it comes to being fast; it’s 28 bucks, so close to free; and because it’s Microsoft it will be ubiquitous. So for us, it’s good. The problem is it took them too darn long to get it out. Working with Microsoft has been a little bit like having a ring through the nose of the bull. We have a rope tied to that ring because we’re ahead of them on this thing, but when they charge I’m going to get out the way and point them at VMware.

GigaOM: But will Hyper-V compete with the Citrix server virtualization business anyway?

Crosby: You should look forward to interesting announcements of products to add value to Hyper-V. We’re going to sell into that footprint much like Citrix has always extended the use cases of Microsoft products.

GigaOM: What about VMware?

Crosby: We only have a 4 percent or 5 percent share in this market, and the market is significantly overpaying for what they have today, so it’s a very, very interesting time. We’re going to track VMware down with the fast, free, compatible and ubiquitous hypervisor and sell on top of that. We’ve accepted that hypervisors are not the stuff you can charge for. It has taken longer than I thought to get there, and customers have yet to decide, too, if the hypervisors are part of the box or in the operating system. We’ll be wherever we can to create for ourselves the largest possible upsell with other products.

GigaOM: So we’re early on in this game?

Crosby: Virtualization is reorganizing the IT industry. Separating the software from hardware allows more services oriented on the software stack. It creates this huge power vacuum in the industry, and everyone is rushing to fill it. Virtualization becomes a tool for differentiation for a former commodity box maker. Look at our deal with Symantec and its Veritas products. That’s a profoundly important play because, in the enterprise, what you’re about to see is companies entering the virtualization market with a commodity hypervisor and a clear intent to upsell the products.

GigaOM: What will virtualization mean for storage?

Crosby: With Xen, multiple servers will automatically pool, and from these resource pools customers get dynamism and availability. VMware turns the storage industry into a dumb block of boxes, while we have a storage model that allows us to leverage our software to the let the storage infrastructure participate in the value chain, and the storage industry works with us very closely. Microsoft is completely missing from storage.

GigaOM: What about desktop virtualization? Unlike the server side, you guys have a lot of competition ready to pounce.

Crosby: Yes, and that opportunity is of great interest to both of us. Arguably the remote delivery of apps is what we have been doing for 18 years at Citrix. We have always cared about the line of sight between an app in the data center and the desktop. We’re very confident and have opened up the category, but everyone and their dog are in there too. We’re watching 10 to 12 other offerings, but we just see a lot of smoke and not a lot of fire.

GigaOM: After storage, where is virtualization heading next?

Crosby: There’s a lot happening with I/O virtualization and the creation of these fabrics for information flow. Fibre Channel won’t roll over and die, but some of the Ethernet stuff is really interesting. Backing away this thing that has always been proprietary presents interesting opportunities. When you virtualize the resources of a single compute memory you create a new type of system where Xen is the virtualization engine, because it’s not proprietary.

GigaOM: So you’re describing a cloud?

Crosby: To the extent that the clouds are relevant, the largest virtualization effort is Amazon Web Services. Xen will be in every cloud. The only cloud that it won’t be in is Microsoft’s and that will be running Hyper-V. So that’s an interesting path as clouds become an opportunity for some IT functions to be outsourced.



Whilst I would agree with Simon Crosby about Xen’s competitive edge versus VMware, here are our thoughts on why we as a cloud infrastructure provider chose Linux KVM over either of these products. I’ll include the following more detailed thoughts on why our choice of KVM and AMD EPT/Intel NPT is superior to Xen/VMWare and Intel VT-x/AMD-V.

Increasing hardware virtualization support:
– Historically, virtualization platforms used software to trap and simulate certain instructions, memory management and I/O in the host virtual machines. VMWare was an early leader in this software technology.
– With the first generation of hardware virtualization, the VT-x/AMD-V extensions trapped these instructions in hardware, giving a significant speed improvement. However, virtualized memory management and I/O remained bottlenecks. Xen was an early proponent of paravirtualization, which attacks those bottlenecks by modifying the host operating system at compile time.
– With the second generation of hardware virtualization, the NPT/EPT extensions minimize the memory management bottleneck. As a result, MMU paravirtualization is a legacy approach, leaving just scheduling and I/O to be virtualized in software by a hypervisor. (I/O virtualization requires a good set of device drivers for the underlying hardware, of course: an area in which Linux excels.)

Hypervisor architecture and device drivers:
– Linux KVM is a hypervisor which is built into mainline Linux. It uses the full range of hardware virtualization support, and directly uses the regular Linux scheduler and I/O device drivers.
– Xen runs an external hypervisor for scheduling, and uses a modified Linux kernel in domain 0 to provide device drivers.
– VMWare runs a proprietary external hypervisor, which includes scheduling and device drivers, many of which are adapted from Linux.
– We believe the KVM architecture is superior to both Xen and VMWare, since the mainline Linux scheduler and device drivers are both extremely well designed, widely deployed, professionally maintained and throughly tested, to a level likely well above what a single company can achieve on either their own proprietary codebase or locally maintained fork of Linux.


Any comments around the patent infringement lawsuit brought on by 01 Communique and the implications to Citrix – how material is the patent claim to Citrix’s strategy?

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