VDI Provides Flexibility, but at a Cost
Virtual desktop infrastructure (VDI) may be the most flexible way to deploy remote desktops, but traditional terminal servers win on cost, a remote desktop specialist asserted in a talk at Microsoft's Tech Ed conference this week in New Orleans.
"Terminal server is the best technology if what you have in mind is the lowest total cost of ownership," said Benny Tritsch, the chief technology officer for Immidio, a German firm specializing in remote desktop products and consultations. "The VDI environment is best when personalization is needed."
The benefit of supplying a desktop to the user over a network, as opposed to maintaining a standalone personal computer for each worker, has long been touted by consultants and the trade press. And Tritsch recounted a few of the major virtues of this approach: Remote sessions allow "the data to follow the user," he said. In some cases, applications can even run faster remotely than they would on a regular desktop computer, thanks to their closer proximity to data sources. And the operating systems are a lot easier for administrators to manage from a central location.
In the past few years, VDI has proved to be an intriguing alternative to traditional terminal servers when it comes to the job of remotely providing desktops to users.
With traditional terminal servers, such as Citrix's XenApp and Microsoft's Remote Desktop Services (a feature of Windows Server), a server can spin up multiple desktops that can be accessed by a remote client machine, either a thin-client device or a full PC. With VDI, as offered by VMware, Parallels and others, a full operating system is encapsulated within a virtual machine, and is streamed to a user remotely.
VDI has a number of advantages that terminal servers have a tough time matching, Tritsch said in his talk.
For one, more applications can run in VDI, he said. Not all applications can be installed in a terminal services environment, due to the fact that they require full access to the operating system, not just to what the user can access.
For its own Remote Desktop Protocol (RDP), which powers a number of terminal services, Microsoft has developed a workaround to redirect system call requests, though "some of the applications still may not work correctly," Tritsch said.
Applications in a terminal server environment can also have issues when it comes to graphic displays. Flash typically cannot be rendered through RDP by traditional means (though the upcoming RDP version 7.1 will address this issue). Some applications that use the Windows Presentation Foundation, which needs to interact with a graphics processing unit, also will not work in terminal server.
Because of such issues, "Most times, Windows 7 platform in a virtual machine is a lot better when it comes to application compatibility," Tritsch said.
Network latency can also be a problem for terminal servers, especially with wide area networks. "Microsoft says very clearly that as soon as you have more than 50 milliseconds' latency, RDP does not perform very well," he said. As a result, terminal services work best on a local area network, though he said all the terminal server vendors are working quite hard to address this problem.
But while VDI offers advantages over terminal servers, using the technology comes with a cost as well.
Most notably, VDI is harder to install than a terminal server setup, especially in large deployments. One might assume that a VDI deployment would be similar to a terminal server setup, but it actually is more complicated.
"Even if you are a seasoned IT pro, you will need step-by-step guides," Tritsch said. There are fewer IT specialists in this field than those dedicated to setting up and managing terminal services. Because of its complexity, VDI is difficult to learn.
"Today, it's extremely hard to find people who can do" VDI, he said.
Also, at least for large-scale deployments of VDI, you will need additional management software, which can significantly raise the cost of the deployment. "In a large environment, you will need some management tools," he said.
As a result of these factors, Tritsch recommended using terminal servers for those cases where the organization needs to deploy a large number of identical desktops at the lowest cost possible, such as for task workers. But if the organization wants its desktops to be more flexible, such as having the ability to run new kinds of applications, VDI would be the way to go.
Tritsch's recommendations are in line with Microsoft's own stance on the subject, which the company articulated earlier this year in a blog post on the subject. Gavriella Schuster, senior director of the Windows commercial product management group, recommended VDI for certain uses, though cautioned it may not be a suitable approach for an entire organization.
"Virtual desktops are not good for all users, though they are good for all organizations," Tritsch said.