Few technologies have become a fundamental part of the data centre as quickly as server virtualisation. That's because the basic value proposition is so easy to grasp: When you run many logical servers on a single physical server, you get a lot more out of your hardware, so you can invest in fewer physical servers to handle the same set of workloads. It almost sounds like found money.

The details, of course, are more complicated. The hypervisor, a thin layer of software upon which you deploy virtual servers, is generally wrapped into a complete software solution that incurs some combination of licensing, support, and/or maintenance costs (depending on which virtualisation software you chose). And you very likely will need to upgrade to server processors that support virtualisation.

On the other hand, reducing the number of servers yields indirect cost savings - less space to rent, less cooling to pay for, and of course lower power consumption.

Even more compelling is virtualisation's inherent agility. As workloads shift, you can spin up and spin down virtual servers with ease, scaling to meet new application demands on the fly.

The path to rolling out a virtualised infrastructure has its share of pitfalls. You need to justify the initial cost and disruption in a way that does not create unrealistic expectations. And you need to know how to proceed with your rollout, to minimise risk and ensure performance stays at acceptable levels.

Making the case for server virtualisation

It's pretty easy to sell server virtualisation. Who doesn't want to get the most possible use out of server hardware? In fact, the basic idea is so compelling, you need to be careful not to oversell. Make sure you account for the likely capital equipment, deployment, training, and maintenance costs. The real savings achieved by virtualisation, as with so many other new technologies, tend to accrue over time.

Most virtualisation deployments require new hardware, mainly because hypervisors require newer processors that support virtualization. So the best time to roll out virtualisation is when you need to add servers to your existing infrastructure or when it's time to replace aging hardware.

The superior efficiency of newer servers will help make your case. Begin by calculating the power consumption and cooling levels the current infrastructure requires. (Ideally, this should be conducted on a server-by-server basis, which can be time-consuming, but will result in far more accurate numbers.) Then check the same specs for the hardware you plan to buy to get an idea of any power and cooling cost savings.

Add the fact that you will be using fewer physical servers for the same workloads, and your proposed virtualised infrastructure will look very, very good compared to the existing one. If the new hardware is sufficiently powerful, you may be able to run many logical servers on each physical unit.