EXPERT RESPONSE
There are several virtualization vendors in the software marketplace today. Deciding which virtualization vendor to recommend to clients is not an easy task. The decision should be based on the best fit for the VAR and the client. The main reason virtualization is so attractive to companies is that they can run multiple servers on the same physical box, which reduces both fixed hardware and ongoing power costs.
Many companies choose virtualization over system consolidation because there is no other way to limit the resources each application will use. For example, a SQL Server performance problem on one SQL Server instance can degrade performance on all consolidated SQL Server instances running on that box. With virtualization software it is possible to limit the resources each virtualized server can use.
SQL Server 2008's Resource Governor feature allows you to place such limits on user processes and applications, which will make the choice of consolidation over virtualization more complex. Windows Server 2008 also will ship with virtualization features that will make the choice even more complex. At this writing Microsoft has not updated Microsoft Virtual Server and is working on the virtualization components that will ship in Windows 2008 in February 2008.
The choice over one vendor of virtualization software over another should be based on stability of the product, performance, features, support and cost.
In the relational database management systems (RDBMS) space, VMWare is working hard to produce a virtualization solution that will be able to support Very Large Databases with minimal performance degradation. Currently all RDBMs running virtualization products will experience some degradation, and mission-critical databases should be carefully evaluated to see how these RDBMs work on each vendor's virtualization software and whether the performance degradation is acceptable.
The decision between VMware and Virtual Server is frequently made on the basis of cost and support. Study the licensing costs carefully. For most VARs and their clients, Microsoft's Virtual Server is cheaper. However, VMware currently offers a much larger feature set than Microsoft Virtual Server, and for larger virtualized environments customers seem happier with VMware than Virtual Server. For smaller virtualized environments, customers in my experience prefer Virtual Server.
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