NetApp has also embraced solid-state drives (SSDs) with its Performance Acceleration Module (PAM), a solid-state secondary cache that Freeman said will eventually become a flash implementation. "We see the benefit of using secondary memory to enhance performance without adding more disk drives," he said.

The idea of slowing down or stopping disk drives when they're not in use was popularized by Copan Systems with its Revolution line of disk-based backup systems that use massive array of idle disks (MAID) technology.

In Copan's arrays, disks are shut down completely when they're not needed; and because only a handful of disks may be active at one time, you can cram many more disks into a single array. Running all of the densely packed disks would suck power and generate excessive heat, but MAID significantly reduces power and cooling requirements.

Other vendors use similar approaches, but some don't shut down disks completely. By reducing power to disks or parking their read/write heads, power consumption is reduced, but the disks can spin up to operational speed relatively quickly when needed. For example, EMC Corp. offers policy-based drive spin-down in its Clariion CX4 arrays and Disk Library backup systems that puts inactive drives in sleep mode.

Nexsan Technologies Inc.'s AutoMAID, available with its SASBeast and SASBoy arrays, also uses policies to spin drives down in three stages -- each stage offers greater power savings but also requires more time for the drive to get up to speed again.

Copan, EMC and Nexsan are just a few examples of disk system vendors that slow or stop disks to save power; many array vendors offer similar capabilities.

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Other vendors are also focusing on ways to save power. GreenBytes' Cypress NAS appliance for archiving long-term data aims to cut energy consumption up to 80%, while Enhance Technology's products feature virtualization and auto spin-down RAID controllers. And last May, EMC Corp. unveiled virtual tape libraries (VTLs) featuring data dedupe. Moreover, EMC's Clariion CX4 storage arrays, which Dell also sells, released with built-in spin-down capabilities.

As for Dell, most of its energy-efficient focus has been on utilization, tiering, spin down and solid-state drives.

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