At the Citrix Synergy show in San Francisco, the announcement of Citrix XenClient rocked the brave, new world of desktop virtualization. With XenClient, Citrix has beaten virtualization leader VMware to the punch with a client hypervisor, available today for download in a "test kit" version.
What is a client hypervisor, and why are Citrix and VMware so hot on it? Basically, client hypervisors have the potential to jump-start adoption of desktop virtualization, whereas business user desktops are centrally maintained and secured in the data center and accessed over the network -- vastly reducing overhead and boosting security. In a briefing before the Synergy show, Citrix senior vice president Wes Wasson exaggerated only slightly when he called desktop virtualization "the hottest area in all of IT."
Desktops on servers?
So far discussions of desktop virtualization have been dominated by VDI (Virtual Desktop Infrastructure), where each user's virtual machine -- which includes the operating systems and any desktop applications -- runs on the server. This requires not only beefy server hardware but sufficient network bandwidth. And when users disconnect from the network, the virtual machine goes away.
With a client hypervisor such as XenClient, the VDI server can deliver a copy of the user's virtual machine over the network to the client, where it runs in its own partition. Think of that virtual machine as a virtual and highly secure business desktop, which can run alongside yet completely separate from a user's personal desktop environment. Users get the best of both worlds: access to the server-based desktop from any location and any device, plus the option to take it with them when they go offline.
One reason the client hypervisor could be disruptive, however, is that you don't need heavy duty VDI infrastructure for it to work. User virtual machines could be centrally configured and managed using more traditional tools, with access to virtual machines controlled through central policies and encryption. And if the client hypervisor approach is a substitute to VDI rather than a complement, where does that leave VMware?
Hyping the client hypervisor
The trouble is that, as the name suggests, the XenClient test kit is a very early release. "It's really just about getting the technology out there and getting it into the hands of the IT pro and letting them kick the tires a little bit," says Burton Group Senior Analyst Chris Wolf about the XenClient download available today. "There's still a lot to do with client hypervisors before they're mainstream desktop virtualization solutions."
One problem is the breadth of hardware supported. At this point we know that XenClient will run only on Intel processors with VT (Virtualization Technology). "Right now they are supporting some of the mainstream desktop platforms from the big three OEMs: Dell, HP, and Lenovo," says Wolf. Compatibility will eventually have to be much broader; no company would pay to rip and replace its desktop fleet in order to roll out desktop virtualization.
And the compatibility issue descends to the device driver level. Like Windows, a client hypervisor installs on bare metal -- each Windows virtual machine runs as a guest. So Citrix faces the same problem as Windows: It must have drivers of some kind for all manner of hardware devices in a system. So-called passthrough drivers can hand off the problem to the guest Windows virtual machine, but no one knows yet how well that will work.
Another compatibility issue is the range of guest operating systems XenClient will support. According to Wolf, "Windows 7 is supported, Windows XP is supported ... beyond that I'm not really sure. I know some folks who have been part of the beta program have had success virtualizing a number of guest operating systems ... I believe even Linux in some cases, but that's not officially support by Citrix at this point."
Still to come: robust virtual desktop management
The other big question is: What management capabilities will Citrix built around XenClient? The potential is huge.
Golden images could be managed on central servers (with much less expense than VDI), where updates and patches are centralized and pushed to client-side virtual machines when users connect to the network. A policy server could be used to control whether the virtual machine could access printers or USB devices, whether the virtual machine could be used offline or only when authenticated to the corporate network, whether the virtual machine is encrypted, and whether the virtual machine would be expired/erased after a certain length of time without connecting to the network.
But so far, says Wolf, such sophisticated management does not appear to be in evidence. "They've built in some basic replication right now, so I can replicate that virtual desktop back to my data center. So for business continuity purposes I can either connect that virtual desktop to a server and run it off a server, or I can just re-synch it with another desktop running the XenClient."
The promise of VDI is to provide the familiar, rich, isolated personal desktop experience to users via a thin client, while giving IT central control over access and data. The client hypervisor has the potential to provide much the same level of central control and all the familiar benefits of virtual machines, including easy backup, copy, and replacement. But XenClient is not even close to being there yet. In fact, at this time we have no way of knowing whether VMware might be further along -- and has just chosen to wait until its offering matures.
According to Wolf, the organizations evaluating client hypervisors believe it will be "2011 or 2012" before they start to look seriously at any major initiatives. The announcement today offers mainly exciting potential.