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New tools and metrics
Some vendors, including EMC Corp., Hewlett-Packard (HP) Co., IBM Corp. and Sun Microsystems Inc., are starting to provide tools that measure power consumption at the device level to manage energy the way they manage other aspects of storage. New energy metrics are also entering the storage lexicon. Kilowatt (kW) and kW/hour are standard energy metrics. When applied to storage, you get kW/TB. A more common metric at this point is kW per rack (kW/rack). Due to increased density, data centers today are pushing beyond 4kW/rack; by 6kW/rack, they're getting into a heat danger zone.
An individual drive uses 5 watts to 15 watts of power depending on its capacity, rotation speed, form factor and operating state, but "you can't just multiply the number of drives in an array by some average power rating to get a total," says Mark Greenlaw, senior director with storage marketing at EMC. The power consumption of the array is more than the sum of the power used by the individual drives. Controllers and other components consume power. Copan Systems proposes two metrics for archival data storage: storage density measured in terabytes per square foot (TB/sq. ft.) and terabytes per kW (TB/kW).
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nagers also need to consider SAN switch power and cooling. Switches consume less power in the data center than servers or storage mainly because there are relatively fewer switches. Still, the power consumption of a switch is significant. "A large switch will use 1,000 watts [1kW] or more," says Ardeshir Mohammadian, senior power systems engineer at Brocade Communications Systems Inc. Higher port density and performance increases switch power and cooling consumption. Don't be surprised to see kW/port and kW/gigabyte per sec metrics soon.
Energy bills--now running at $60/sq. ft. for the data center, according to Gartner's Bell--currently go to the facility manager or CFO, not to the storage manager. Data center space is handled by the real estate department. To lower energy costs, there needs to be more coordination among the disparate departments.
As energy costs and consumption rise, new tools--from low-power chips to digitally addressable power supplies that can regulate power to the device's changing requirements--are being developed to more effectively manage energy. Power, cooling, space and disposal are becoming integral, closely watched parts of the TCO analysis for every storage device the organization buys.
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