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Understanding your options for desktop virtualization

Virtual desktops may not save money, but they offer other benefits. This part of our desktop virtualization handbook examines what virtualization technologies can do for you.

Before you jump on the desktop virtualization bandwagon, you need to figure out whether your organization can benefit from the technology. In this second segment of a four-part e-book Desktop Virtualization From A to Z, we'll help you understand the different types of desktop virtualization -- it isn't all VDI.

The first step to sorting out the plethora of desktop virtualization options is understanding what desktop virtualization is and what it isn't.

At the most fundamental level, virtualization is the separation of the physical from the logical, so desktop virtualization is the separation of the physical client device from the management of the OS. When most people hear the term desktop virtualization, they immediately think "VDI!" Note that virtual desktop infrastructure is just one type of desktop virtualization.

In fact, the technology can be any of the following:

  • VDI. Despite the term's literal meaning, IT today uses it to mean "Windows desktops running as virtual machines in a data center, with users connecting from thin clients or desktops with client software." VDI is similar to terminal server (and Citrix) solutions, and VDI and terminal servers share many components, such as remote display protocols and client software. Some people consider VDI to be nothing more than a "single-user terminal server."
  • Terminal server. Well, if VDI is just a single-user terminal server, we have to include Terminal Services (and products based on it, such as Citrix's XenApp and Quest vWorkspace) to also be a form of desktop virtualization.
  • OS streaming. There's a growing trend in which network-connected client devices (most often physical desktop computers) boot up from a disk image mounted across the network instead of from a local hard drive. This is called "OS streaming" and is made possible via products such as Citrix Provisioning Server, Double-Take Software's Flex and Wyse Technology's Streaming Manager. OS streaming is great because it's not virtualization in the classic sense -- there's no hypervisor -- so the clients perform at full bare-metal speed. With OS streaming, updating a client is as simple as updating that single disk image, which can be shared across many clients, on a network share.
  • Client-based virtual machines (Type 2 client hypervisors). Desktop virtualization doesn't always have to involve a network. Many companies deliver complete virtual machine (VM) disk images that users run locally on their laptops. This is nice because admins have to worry only about their images and not the entire laptop stack, and users can install whatever they want natively on their host laptops without breaking the locked-down corporate VM.
  • Client hypervisor (Type 1 client hypervisor). This is another form of client VM. One of the latest trends is to replace the OS on a laptop altogether with a hypervisor that runs one or more VMs. This is similar to the previous option, except that users don't have access to the root OS. Client hypervisors typically work better in environments where the IT department has full control over the users' hardware.

As you can see, desktop virtualization is much bigger than any single technology. And while the ability to choose from many options is great, most organizations still need a combination of traditional desktops plus one or more of these virtual desktop solutions.

Desktop virtualization is bigger than any single technology. Most organizations need a combination of traditional desktops, plus one or more of these virtual desktop solutions.

Unfortunately, no one product on the market satisfies all these scenarios. VMware, which has shown great leadership with server virtualization, hasn't demonstrated the same leadership with desktop virtualization. VMware's View can be used only for VDI and client-VM scenarios.

While certainly ahead of VMware, Citrix Systems Inc. doesn't offer a complete picture either. Citrix's XenDesktop enables VDI, terminal server and OS streaming from a data center, but it requires VMs to run on the client via a hypervisor called XenClient. The company doesn't offer anything that allows simple corporate VMs to run on top of existing laptops.

Quest Software's vWorkspace is a strong product too, even though it offers only VDI and terminal server support, with no direct support for streaming or any type of client VM.

In addition to the more complete products from the Big Three, there are literally hundreds of desktop virtualization offerings from other vendors, big and small.

For client VMs or client hypervisors, check out software from RingCube Technologies, MokaFive, Virtual Computer, Virtual Bridges and Wanova. To manage applications in your virtual desktops, consider Microsoft App-V, Citrix XenApp Streaming, VMware ThinApp, Symantec Workspace Virtualization, Xenocode, InstallFree and Endeavors Technologies. These technologies allow you to virtualize and deliver apps throughout your entire environment, both physical and virtual.

And for managing the user environments across your physical and virtual desktops, consider products from AppSense, RES Software, Scense or triCerat. These products, which began life a decade ago as "profile managers," have grown to manage the entire user environment, including profiles, applications, data and other settings. They can be used to bridge the gap between physical and virtual desktop environments -- and between Windows XP and Windows 7.

So, just as there is no single virtualization technology that will work for all desktops in a company, there's also not one product that will work for everyone. Luckily, a lot of great stuff on the market can meet whatever need you have.

Brian Madden
is an independent industry analyst and blogger, known throughout the world as an opinionated, supertechnical desktop virtualization expert. He has written several books and more than 1,000 articles about desktop and application virtualization. Madden's blog, BrianMadden.com, receives millions of visitors per year and is a leading source for conversation, debate and discourse about the application and desktop virtualization industry. He is also the creator of BriForum, the premier independent application delivery technical conference.

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