Evaluating Your Options for Desktop Virtualization (Part 1)

If you would like to read the other parts in this article series please go to:


A couple of years ago, Virtual Desktop Infrastructure (VDI) was considered to be impractical and cost prohibitive for all but the largest organizations. Today however, VDI has become much more accessible thanks to hardware advances and much more innovative approaches to VDI. The goal of this article series is to talk about some of the options that are available to organizations who are considering implementing VDI. As I do, I will address the pros and cons of each approach.

Before I Begin

Before I get started, I wanted to quickly define VDI for the benefit of anyone who might not be familiar with the technology. VDI, or Virtual Desktop Infrastructure, is a technology in which a server is used to host desktop operating systems. This technology is similar to what is used for server virtualization, except that there is usually a mechanism in place to link users to individual virtual desktops so that each user is connected to a different virtual desktop. This ensures that you will never have a situation in which two users attempt to simultaneously connect to the same virtual desktop.

The other thing that I want to say before I get started is that there are a lot of different desktop virtualization solutions on the market, and there is no way that I could possibly talk about all of them. That being the case, I am going to use a representative sampling of virtual desktop products. As such, please do not E-mail me to tell me that I forgot to talk about a certain product.

The Windows Remote Desktop Services

I want to begin my discussion by talking about the Windows Remote Desktop Services. I am starting with this particular technology because it is built into the Windows Server 2008 and Windows Server 2008 operating systems. Keep in mind however, that even though the Windows Remote Desktop Services are integrated into the Windows Server operating system, it doesn’t mean that the Windows Remote Desktop Services can be freely used as a VDI solution. There are some additional licensing costs that come into play. I will discuss the licensing requirements at the conclusion of this article.

Remote Desktop Services VDI Components

Organizations using the Remote Desktop Services (RDS) as a VDI solution must typically deploy several servers, each of which performs a different role. The first server role that might be required is the RDS Gateway. The RDS Gateway service is used to link remote (Internet) users to a VDI session. The RDS Gateway server is only required if external users will be accessing the VDI infrastructure.

The next server role that is required is the Remote Desktop Connection Broker. This is a primary RDS role that is required regardless of whether users are connecting remotely or are connecting through the local network. As you can see in Figure A, remote users connect through the RDS gateway which then proxies the connection to the Remote Desktop Connection Broker. Local users establish a connection directly to the Remote Desktop Connection Broker.

Figure A: This is the architecture used by an RDS based VDI Deployment.

As you can see in the figure above, the Remote Desktop Connection Broker is a central component in the VDI architecture. The Connection Broker functions in a slightly different manner depending on the type of session that is being requested.

In an RDS based VDI environment, there are two different types of virtual desktops that can be created. In most cases, users connect to a pool of identical virtual desktops. When a user connects to a desktop within the pool, they are allowed to use the desktop for the duration of their session, but they never actually own the desktop. When the user logs out the virtual desktop reverts to a pristine state. However, administrators also have the option of creating personal virtual desktops. A personal virtual desktop is a virtual desktop that is “owned” by a specific user. Any changes that a user makes to their personal virtual desktop are retained from one session to the next.

If the user attempts a connection to a personal virtual desktop then the connection broker locates the requested virtual desktop and makes sure that it is turned on. If the requested virtual desktop is powered down then the connection broker turns on the virtual desktop and then connects the user to it.

If the user is attempting to connect to a pool of shared virtual desktops then things work a bit differently. The Connection Broker connects to the Remote Desktop Session. Normally the Remote Desktop Session Host is used for running remote apps. However, in a VDI environment the server is configured to work in redirection mode, which prevents anyone other than the administrator from running remote apps on the server. Instead, the session host is used to determine whether or not the user currently has an active session. If the user has a disconnected session then the session is reconnected. Otherwise, a new session is created and a virtual desktop (which is running on a group of Hyper-V servers) is assigned to the user.

Pros and Cons

Like all VDI solutions, there are both advantages and disadvantages to Microsoft’s approach. The primary advantage is probably that most of the required components are built into the Windows operating system, so the solution is well documented and fully supported. The solution is also designed to be scalable.

The primary disadvantage to taking this approach to VDI is the cost. Not only will you need a lot of hardware, but the licensing costs can be excessive. For starters, you will need a Windows Server license for each instance of Windows Server. In smaller scale deployments it may be possible to reduce the Windows Server licensing costs by running the Connection Broker, Session Host, and RDS gateway on virtual hardware. Windows Server 2008 Enterprise Edition is licensed to allow for up to four virtual machine instances at no extra cost.

In addition to the Windows Server licenses, you will also need Client Access Licenses for each user or device that connects to your VDI infrastructure. There is also a Remote Desktop Client Access License (RD CAL) that is required for each device. However, the RD CAL also allows licenses the organization to use App-V, Microsoft’s application virtualization solution.

In addition to these licensing requirements, there may be other licensing requirements that also come into play. For instance, you may be required to license the desktop operating systems that are run by your RDS clients. You will most likely also need to license some management tools. For example, it can be difficult to manage a RDS VDI deployment without System Center Virtual Machine Manager and System Center Operations Manager.


Although the Remote Desktop Services are Microsoft’s best known solution for VDI, there are other solutions available. In Part 2 of this series I will discuss a lower end Microsoft VDI solution called Microsoft MultiPoint. As I do, I will compare its cost and functionality with that of the Remote Desktop Services.

If you would like to read the other parts in this article series please go to:

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