That's because any space and energy savings that may be achieved through server virtualization and consolidation could be outweighed by the vast numbers of new servers that will be required in the data centers of organizations embarking on the virtualization of end-user applications or entire end-user desktops.
"Technologies like VMware's VDI (Virtual Desktop Infrastructure) need a huge amount of hardware like servers, storage and SANs in the data center," warned Ronni Colville, a vice president and distinguished analyst at research house Gartner. For companies already at the limits of their data center's capacity, this could be a serious problem.
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But the benefits of virtualized desktops are in some circumstances quite compelling: It's easier to manage PC images in a data center than physical machines that are far apart, and data is easier to manage and back up when stored centrally.
"When we are talking about call centers, trading floors and setups where there are large numbers of people and plenty of bandwidth, this type of technology can be ideal, " she said.
But there's much more to end-user virtualization than virtualized desktops, so even in circumstances where something like VDI may not be appropriate (e.g., for mobile workers with intermittent Internet connectivity or staff in branch offices connected by a slow WAN link), the data center is still likely to feel an increased burden.
There are two reasons why: application virtualization, and application streaming. Actually the two are intimately related, and both are likely to be the cause of a great deal more server side action in the future than we have seen in the past.
Before we look at what they are, it's worth thinking about why virtualization for end-user applications is becoming practical in the first place. The answer comes down to the new processors, which include Intel's VT and AMD's AMD-V virtualization technologies that modern PCs are equipped with, according to Brian Gammage, a vice president and fellow at Gartner.
"Intel and AMD have changed the x86 architecture with these technologies by adding four new levels of privilege. This is by far the most significant change in the x86 architecture to have taken place in the last quarter century," he said. As a result of these technologies, most operating systems can be run unmodified on top of a hypervisor.
Simplicity is driving end-user virtualization, according to Gammage. "Virtualization helps resolve the issue that PCs are too complicated," he said. "On the desktop, virtualization is the masking of physical resources. What it does is decouple the hardware, the OS and the applications. By interposing a thin layer of software, any level can be changed without having an effect on any other."
So instead of an organization having multiple PCs of various configurations running a variety of OSes and different versions of different apps, they are decoupled. We're then talking about a virtualized PC, running a bubble of software containing an OS and applications, or a bubble containing the OS and separate bubbles running separate applications.
What Are the Benefits?
Virtualizing the physical PC itself is not essential, but it does make things considerably simpler for a large organization if OSes and apps are targeted to run on a standardized piece of virtual hardware instead of a multiple PCs with different configurations. Putting the OS and apps in their own bubbles makes a great deal more sense.
"Application virtualization can help solve many problems," Gammage explained. "For example, it can be valuable if you are moving OSes, perhaps to Vista. Normally you have to do regression testing to make sure all your combinations of apps work together. But you can remove the links between all your apps altogether by virtualizing them, and we are seeing a lot of interest in that right now."
This begs a very interesting question, he points out. "Do I have to leave the application bubble on the desktop, or could I not store it in the data center?" The answer is that since everything is modular, it is irrelevant where the software resides. The virtualized application bubbles can live on the PC, or they can live in the data center, or they can be streamed from the data center to the PC whenever they are needed.
Streaming virtualized apps is interesting because it caters to mobile users who may not always be able to connect to the corporate network or who may be able to connect only over a slow, low bandwidth WAN. Apps are stored on a server, but executed locally.
When you use app streaming, you can chooses to cache an app in other words to retain the bubble on the mobile user's computer so it can be used offline. When an application is launched when the user is online though, it can call home and check for any updates and pull them down the wire. The point is, before there was an all or nothing approach, with applications run locally, or applications hosted on a server. Now we can be more flexible, and for that reason I think we will be centralizing more.
Who provides the technology to do this? It's no surprise that the big players include VMware with its VDI product for complete hosted desktops, Citrix with XenDesktop for virtualized desktops (using virtualized apps) and XenApp (formerly Presentation Server)for application delivery and virtualization. Others players include Microsoft with Application Virtualization (formerly SoftGrid Application Virtualization), Symantec with its Appstream application streaming technology and Altiris SVS application virtualization technology.
Ultimately, Gammage believes it's likely application streaming and application virtualization will converge. As virtualization becomes more popular this will mean more server side computing, more servers in the data center, and more power and space requirements. The benefits in terms of increased agility security, reliability and manageability may be great, but they'll be possible only if you have the capacity in your data center. In other words, you may have to make some room for this type of virtualization by carrying out some server virtualization and consolidation first.