The US Environmental Protection Agency recently proclaimed that datacentres consumed 61 billion kilowatt-hours of electricity in 2006. That's roughly 1.6 percent of total US electricity consumption and is worth about $4.5 billion.

Assuming current trends continue, by 2011 the national energy consumption by datacentres is expected to nearly double, making energy efficiency a top priority for CIOs.

One technology that can help companies increase efficiency is virtualisation, which can play multiple roles in the datacentre.

Virtualisation makes it possible, for example, to divide a single server into smaller virtual servers, or pool smaller, individual machines so they can perform as one larger system. Gartner estimates that more than 90 percent of companies using virtualisation are doing so to reduce x86 server space and costs. In fact, the company estimates that virtualisation cut the x86 server market by four percent in 2006.

Power savings can be even greater when addressing storage assets. Storage resources - which IDC says are growing 50 percent per year - are among the largest consumers of energy in the datacentre, in most cases consuming 13 times more power than processors. What's more, use of storage assets is often 25 percent or less, making this environment almost as inefficient as x86 servers.

Storage virtualisation can drive up use rates from 25 percent to 60 percent or more.

Applying virtualisation technologies across all system assets, including servers, storage and network devices, can allow companies to tap into unused capacity without adding resources that draw more power. The most energy-efficient equipment is equipment that's no longer in use, whether it's a server, a router or a storage device.

Achieving that, however, requires centralised management of virtual and physical devices, because, while virtualisation helps address costs through consolidation of physical resources, it adds complexity by increasing the number of virtual resources that need to be managed.

Gaining a more accurate understanding of the relationships among physical and virtual resources enables administrators to manage the infrastructure in a more integrated, holistic way.

Systems-management virtualisation tools that manage all resources - physical and virtual - can help manage the resources in an integrated fashion from a single dashboard, significantly reducing the number of tools required and the cost of administration to support multiple types of servers.

These tools can also help relocate virtual servers automatically in order to take advantage of lower utilisation rates and help administrators inventory server and storage devices, monitor the health of these devices, manage maintenance and prevent downtime.

However, a common problem organisations face is the difficulty in determining how and for what purposes employees are using virtual resources. To drive a successful energy-efficient program, you should be able to identify which resources are used and whether they are physical or virtual.

IT chargeback methodologies can also help improve IT accountability and resource alignment. Existing tools, for example, can monitor use of applications, servers and other IT resources, so organisations that wish to consolidate and virtualise servers can accurately charge for related use.

Factoring virtualisation into chargeback processes not only enhances the process by more tightly mapping companies' resources to business units, but also allows them to stretch their budgets to focus on energy-efficient programmes.

The energy issue hasn't escaped the attention of power companies or government organisations. More than 80 local utility and state energy-efficiency programmes are offering rebates for increasing energy efficiency.

Pacific Gas and Electric of California, for example, has approved a plan to reimburse part of the costs for server- and storage-consolidation projects, including software, hardware and consulting, up to a maximum of $4 million per customer.

An energy-efficient datacentre is not optional today - it is a necessity. And virtualisation technologies can lead to power savings that result from consolidating hardware and improving utilisation rates, providing you also adopt proper management tools and methodologies.

Rich Lechner is vice president, IT Optimisation at IBM. He can be reached at [email protected].