Calculating carbon neutrality means converting from electricity consumption to Carbon Dioxide emissions. How is this done? 3PAR has a carbon-neutral product programme and Craig Nunes, 3PAR's marketing VP, has described how it makes the vsarious conversions needed to arrive at a carbon emissions value for its products.

1. Disk drive power and cooling

Power: One disk drive consumes approximately 30 watts for power.

Cooling: Cooling figures vary, but according to Gartner's Michael Bell, cooling requirements are equal to the initial power requirements for data entre equipment in a rack drawing 6kw of power, a fairly standard power density for racks. So cooling for 1 disk drive consumes another 30 watts.

Total energy required, therefore, for a single disk drive is 60 watts.

Total energy required for a single disk drive for a year: 1 disk x 60 watts x 1 kilowatt/1000 watts x 8760 hours/year = 525.6 kilowatt-hours/year for 1 disk drive.

To assess the energy requirements globally, 3PAR uses Gartner's Hard Disk Drive Forecast. Disks purchased and used in multiuser systems and storage arrays over the past five years total approximately 108,000,000. This is Craig Nunes' estimate for what is currently spinning in data centres around the world.

Global power demand per year: 108 million disk drives x 525.6 kwH = 56.8 billion kwH

Electricity rates

You can find electricity rates on: http://www.eia.doe.gov/emeu/steo/pub/4tab.html. I use about $0.10/kwH which yields a $5.7 billion cost to power these drives globally.

Disk drive environmental impact

1 kwH yields 1.55 lbs of CO2 emissions.

CO2 emissions are often discussed in tons (2,000 lbs) or metric tons (2,205lbs). The carbon offset we purchase from Terapass is for one metric ton of carbon offsets. From the figures above:

1.55 lbs x 56,8 billion kwH = 88 billion lbs (or 40 million metric tons) of CO2 emissions are generated globally each year in the power and cooling of data centre disk drives.

From the same Energy Star website mentioned above, one car generates 11,560lbs of CO2 emissions per year. In car-terms, the carbon emissions generated by powering and cooling data centre disk drives globally is equivalent to the emissions of 7.6 million cars!

Disk drive impact on energy and the environment

Energy: Power and cooling for 108 million disk drives amounts to 57 billion ilowatt-hours each year.
Environmental impact: The CO2 emissions from these disk drives totals 44 million tons every year.

3PAR customers who take advantage of thin technologies -- Thin Provisioning, Virtual Copy (snapshot), Remote Copy (remote data replication) - have been able to deploy just 1 terabyte of capacity where 2.5 terabytes of traditional capacity had been required. Each terabyte of disk drives roduces about one metric ton of CO2 emissions each year. Therefore Thin Provisioning and the other thin technologies at 3PAR are reducing disk capacity and the associated carbon footprint by approximately 60 percent.

The Carbon Neutral Storage Program offsets the carbon footprint of the remaining 40 percent with a retailer of greenhouse gas emissions called Terapass, thus providing carbon-neutral storage. Terapass sponsors wind energy, biomass and industrial efficiency programs to create offsets for the carbon emissions generated by these disk drives. These reductions in the U.S. are verified by the Chicago Climate Exchange. 3PAR will offset approximately 5,000 metric tons of CO2 emissions in 2007, roughly the equivalent to taking 1,000 cars off the road for a year.

To date, 3PAR customers have allocated about 31 petabytes of usable capacity to their applications. With traditional fat array technologies from the traditional SAN storage market, this would have required approximately 45 petabytes of raw capacity using a mix of RAID 1 and RAID 5. Yet by using 3PAR thin technologies, customers have achieved the same result by purchasing only 18 petabytes of raw capacity.

3PAR claims that, in other words they have saved the purchase of approximately 27 petabytes of raw capacity. Put another way, they have achieved the same business results with 60 percent less storage capacity. This disparity represents an annualised energy savings of approximately US $6.6 million for 3PAR customers worldwide.

In environmental terms, the carbon emissions eliminated by this capacity reduction would equate to nearly 50,000 metric tons of CO2, the equivalent emissions of 10,000 cars for an entire year.