Virtual servers' impact on the network

Brien Posey

There are many virtualisation products on the market. Although the end result is usually similar, each of these products does things in its own way. For the purposes of this article, I will base my answers to the frequently asked questions on Microsoft's Virtual Server 2005. I am doing this because it is one of the dominant virtual server products and because it is the virtual server product that I am the most familiar with.

Where do I get it?

One of the first questions you may be asking about a virtual server is where you can get it and how much it costs. Believe it or not, Virtual Server 2005 is free. You can download Virtual Server 2005 from the Microsoft website.

What is the virtual server's impact on the network?

The short answer to this question is that there is no impact on the network. Virtual servers work just like physical servers when it comes to sending and receiving traffic on the network.

The longer answer to the question is that network performance can suffer if multiple virtual servers share the same physical network adapter. In such cases, the network adapter can cause a bottleneck for the virtual servers. You can easily get around this problem, however, by installing multiple network adapters and setting up the virtual environment so that each virtual machine gets its own network adapter.

Virtual Server 2005 also gives you the option of creating an internal network. An internal network

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is simply a network servicing only the virtual machines. This allows the virtual machines to communicate with one another through a dedicated backbone without having to place packets on the physical network. Keep in mind that internal networks are accessible only to virtual machines.

What happens when the virtual server's workload increases?

Another question that I want to address is what happens when the virtual server's workload increases? As I mentioned in Server virtualisation basics for network pros, all of the installed virtual servers share the physical server's resources. If a virtual server is running an application and the application's workload increases, there can be problems.

Virtual Server 2005 has mechanisms in place to prevent a single virtual server from consuming all of the physical server's resources, so you don't have to worry about one virtual server stealing memory from another. What you do have to worry about is that the virtual machine will no longer have sufficient resources to run the application.

When this happens, there are a couple of things you can do. One option is to reallocate the physical server's resources. For example, you might assign more memory to the virtual machine. Another option is simply to move the virtual machine to another physical server that is not being as heavily utilized. Virtual machines, their operating system, and everything else that they contain all exist within a single virtual hard drive file. Like any other file, a virtual hard drive file is simple to move from one machine to another.

What if a virtual server crashes?

Virtual machines are completely self-contained environments. If a virtual operating system produces a blue-screen error, the crash affects only that virtual machine. The host operating system and any other virtual machines that may be running are all isolated from the crash.

It is important to remember, however, that all of the virtual machines depend on the host operating system. If the host operating system crashes, every virtual machine on the server will also fail.

Are there any licensing issues with virtual servers?

One of the trickier questions that people often ask about virtual servers is how licensing works. Unfortunately, I can't really give you a good answer to this question because licensing requirements vary from product to product. What I can tell you is that Windows Server 2003 R2 Enterprise Edition has been licensed so that each physical server can run up to four virtual instances of Windows Server 2003 R2 without incurring any additional licensing costs.

How do I back up a virtual server?

One of the main reasons for implementing virtual servers is to help reduce the administrative burden. One way the administrative burden is reduced is that the backup process is greatly simplified when virtual servers are used.

As you already know, virtual servers make use of a virtual hard drive, which is nothing more than a file residing on the host machine. You can use Volume Shadow Copy Service to take a snapshot of this file. Doing so allows you to back up the virtual machine in less time and with less effort than is usually involved in backing up a physical server. Because you can use Volume Shadow Copy, restoring a virtual machine to a previous state is also really quick and easy.

Suppose, for instance, that you install a service pack on a virtual machine and then the virtual machine blue-screens. If you made a snapshot of the virtual machine before installing the service pack, you could roll back the machine to its previous state by simply restoring the snapshot.

If you need more information about Microsoft Virtual Server 2005, I suggest visiting the Microsoft Virtual Server 2005 website.

About the author: Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Windows 2000 Server and IIS. You can visit his personal website at