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Want to fight global warming? Try virtualization.

The biggest marketing trumpet for virtualization has been monetary savings--physical-to-virtual conversions reduce capital expense by consolidating many servers onto fewer hosts. Additional potential savings can come from reduced management costs, less downtime, and lighter staffing.

As energy prices have fluctuated widely during the past year, CFOs are punching new holes to tighten corporate belts ever further, looking for savings wherever they can. Power and heating and cooling costs are surfacing as areas of opportunity.

That's all good for a company's bottom line. But in addition to freeing up floor and rack space, large-scale server virtualization can result in significant reductions in electrical and cooling needs. And since most of our power comes from burning fossil fuels, it's safe to say that each server is responsible for tons of carbon dioxide annually. General assessments are 4 to 12 tons of CO₂ per server per year. Are swimming polar bears starting to haunt you yet?

The stats associated with virtualization vary widely, depending on who's making the pitch. For example, Oriel Technologies, an Australian VMware channel partner, proposes that paring 45 servers down to five host servers through virtualization can keep 506 tons of carbon dioxide out of the atmosphere.

I have a hard time visualizing 506 tons of CO₂, so Oriel provides equivalents: planting 2,228 trees, offsetting the annual emissions of 113 cars, or, because they're Australian and it's humorous (and true), offsetting the annual emissions of 219 cows.

Whatever your view on the IT benefits of virtualization or whether you want to argue with the specifics of the assumptions in these estimates, it's tough to argue with the basic premise: Virtualization yields fewer physical servers in your data center. No matter what virtualization host platform you choose, fewer boxes equals less electricity consumed. Less electricity consumed equals fewer emissions.

VMware has taking green savings one step further. Distributed Power Management (DPM) is a new feature of its Distributed Resource Scheduler (DRS) module of ESX (and soon to be part of vSphere.) Relying on VMotion and DRS, VMware clusters can selectively shut down physical hosts as load requirements decrease, further consolidating running virtual machines to a subset of hosts. As loads ratchet up again, offline hosts power back up via wake-on-LAN, and VMs redistribute as more capacity is required. VMware projects an additional 20% power and cooling savings thanks to DPM.

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