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Virtualizing SQL Server: Four questions to ask first

Before virtualizing SQL Server, have you addressed SQL Server support on virtual machines and available hardware resources? This tip outlines four key considerations.

With server virtualization all the rage these days, a lot of people approach me with virtualization-related questionsA frequentquestion is whether it is OK to virtualize SQL Server. The short answer to this question is that virtualizing SQL Server offers the same benefits as virtualizing most other types of servers (better hardware utilization, reduced hardware costs, etc.).


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But before you begin virtualizing SQL Server, have the answers to these four critical questions :

1. Will your SQL Server be supported within a virtual server? Generally speaking, virtualized SQL Server deployments are supported as long as you run SQL Server 2005 or higher on top of Windows Server 2008. You can read Microsoft's official SQL Server support policy.

2. Can your hardware handle the workload? The virtualization process necessarily involves a certain amount of overhead. For lightly used servers, this overhead usually isn't noticeable, but that probably won't be the case for a database server that already uses most of its available hardware resources. Once virtualized, such a server is likely to experience performance problems (assuming that the same hardware is used) because the server will have access to fewer of the available hardware resources than when it had free reign of the server.

3. What is the actual benefit to virtualizing the server? One of organizations' most common reasons for virtualizing servers is so they can save hardware costs by hosting multiple virtual machines on a single physical server. In the case of SQL Server, you may find (depending on the host server's capabilities) that the SQL Server can be virtualized but that the host server lacks the capacity to host additional virtual servers. In this case, consider whether it is worth it to virtualize SQL Server. If your goal is to have the flexibility to move the SQL Server from one physical server to another, then virtualizing may indeed be worthwhile. Otherwise, it may be better to forget about virtualizing your SQL Servers.

4. What are your storage requirements? Most virtual servers are configured to use virtual hard disks. Using a virtual hard disk involves overhead that prevents the virtual hard disk from performing as well as a comparable physical disk. Some virtualization technologies allow you to dedicate physical disks, partitions, or logical unit numbers to a virtual machine to improve the virtual server's disk performance. While allocating such a resource to your virtual SQL Server may be a good idea, refrain from allocating direct attached storage, as this limits your ability to migrate the virtual machine to another host.

As you can see, SQL Server can benefit from being virtualized. But prior to doing so, ensure that your host server is up to the job. As such, capacity planning and performance monitoring are critical parts of the virtualization process.

About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional (MVP) award for his work with Exchange Server, Windows Server, Internet Information Services (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Posey has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit his website at


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