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VDI provides flexibility, but at a cost

A remote desktop specialist reviews VDI and terminal service at Tech Ed

By Joab Jackson, IDG News Service
June 11, 2010 03:32 PM ET

IDG News Service - 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.

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