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You can also keep disks powered off until they're needed. These systems are sometimes called massive arrays of idle disk (MAID). The concept is simple. Some data stored on disks, such as archival data or backups, may be seldom, if ever, accessed. Disks storing this inactive data are powered off to reduce energy costs. When the request to access the data is received, the disks are powered up. When the disks are idle again, they're powered down again.
Some vendors have implemented both technologies in a single disk system. After the initial threshold of inactivity is met, drives are rotated at a slower speed. These drives are then periodically powered up to run diagnostics, usually monthly, to ensure they continue to function properly.
One advantage of tape systems is that their power and cooling requirements are much less than similar capacity disk systems. Tape cartridges, when stored on a shelf or in an automated library, require no electricity. Several vendors now also offer removable disk cartridges that have many of the same properties as tape cartridges. They look like a tape cartridge, but contain a small hard drive within the plastic enclosure. These disk cartridges are inserted in a disk drive reader that powers up the disk drive. After data has been read from or written to the disk cartridges, the removable disk cartridges are then unloaded from the reader and stored within an automated tape library or on a shelf, or possibly transported to a remote
The solutions noted here save energy by spinning drives slower or not at all. But there's another way to save power: store less data. We could ask everyone to delete data they no longer need and aren't required to keep for regulatory compliance. However, many of us feel comfortable keeping old data around ... just in case.
There's an easier way to reduce the amount of data that we store: Use software that recognizes and eliminates duplication. Some software eliminates duplicate files, while others detect duplication at the block level. The amount of data reduction varies greatly depending on the type of data and the data deduplication technology. Some data centers report data-reduction rates of 10:1 or 20:1, while others report triple-digit reduction ratios. Bottom line: Storing less data requires fewer disks and saves energy.
This was first published in September 2007