Best Practices: Pull the plug on high energy costs


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Disk storage engineers, like their server counterparts, are developing new and innovative ways to reduce energy consumption. Lower energy consumption chips are finding their way into high-performance storage arrays that are designed to meet the stringent performance demands of online applications.

Higher capacity, lower cost disk storage (usually populated with SATA disk drives) is commonly used to store application data with less-stringent performance demands and as the target for backup and archival applications.

Because the performance requirements of application data stored on these higher capacity disks are less rigorous than those of mission-critical online applications, engineers have more flexibility in designing energy-efficient storage. Evaluating some of the new innovations in high-capacity disk arrays can help reduce energy costs.

Trimming the tab for storage energy
There's a direct correlation between the number and speed of disk drives and the electricity required to power these devices. It takes electricity to spin up disk drives and continuous power to keep them spinning. If we spin these disks faster, more power is needed. We also need to cool these devices. The more disks there are spinning, the more cooling is required. Reducing the energy requirements for disk systems is therefore relatively straightforward. We must reduce the number of spinning disks or spin the disks at a slower rotational rate. These techniques work

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well to store infrequently accessed data, but the same techniques may wreak havoc with applications that demand fast response times.

Saving energy can be as simple as migrating to larger capacity disk drives. For example, if backups today are written to 250GB SATA disks and we now write those backups to 500GB SATA disks, half the number of disks will be needed and energy--and floor space--will be saved.

Other techniques have been developed to make storage "greener" or more energy efficient. Some storage systems detect when a disk drive hasn't been accessed for several minutes. Once the preset period of inactivity is reached, the drive is "spun down" or rotated at a slower speed to save energy costs. A disk drive designed to spin at 7,200 rpm in normal operating mode may spin at half that speed during its inactive period. When a request to access data on the disk is received, the drive is then "spun up" to its normal speed.

This was first published in September 2007

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