Virtual Server Capacity Planning: Keeping It Real

How many virtual machines should you run on a physical server? If your answer is "as many as possible," it might be time to take a step back.A recent article on CIO.com points out that virtualization capacity planning tools are widely available, and they are sometimes quite useful. Yet the fact remains that sizing a VM server load is rarely a cut-and-dried process. The differences between guest OSes, applications, data I/O, and other factors add up to a situation where planning tools quickly lose their grip on reality.

The article offers some good suggestions about how to conduct real-world virtualization planning, including:

- Don't forget to take differences in processors, server chipsets, and memory into account during the planning process. Simply looking at the number of processor cores available and then multiplying by some magic number might work fine -- or it might result in a train wreck.

- Take a "less is more" approach to virtualization; "too much focus on consolidation inevitably leads to poor performance and user dissatisfaction."

- Pay close attention to the amount of RAM installed on your servers. Both of the experts interviewed for this article agreed that 2-4 GB per core is a very good place to start.

- "Don't forget the plumbing," including storage and networking infrastructure requirements.

- Remember that server sprawl can happen with VMs, too. In fact, the temptation to create virtual servers that are rarely used or simply pointless is a common problem when a company jumps on the virtualization bandwagon.

Don't Miss: NEW! Virtualization How-To Center

Finally, the article suggests taking advantage of the management and configuration tools that are available for a specific virtualization platform. Some of these are vendor-specific, while others are third-party tools that work across platforms. Either way, these tools give you something that too many companies overlook -- detailed knowledge about how they are really using their virtualized systems.