"Lazy disks" as a way of bypassing the "problem of the four nines"

Treehugger: Practicality abounds in IT shops these days; first, we had the realization that 99.9 uptime was good enough for most business applications, preventing us from overspending on hardware. Now several vendors have taken this thinking into the data storage arena, and it's reducing costs and energy consumption dramatically. That's good, because power consumption for data storage will exceed that of all other equipment by next year.

The technology is called MAID (massive array of inactive disks), a rather oxymoronic name. But the technology is sound; it's based on the simple idea that the majority of data doesn't need to be accessed immediately. For example, data that experiences high activity (e.g. real time stock quotes) would require high performance storage, but data that does not experience high activity (e.g. the 1997 corporate report) can reside on lower performance and more power efficient storage. MAID takes advantage of this and turns disks off that are not in use, then powers them back on when an application needs access to dormant data. Think of it as a giant spare closet filled with stuff that you only use occasionally like winter clothes, suitcases, unicycle, etc.

Savings are big - coupled with removing duplicate data (the typical organization may have between 10 and 30 copies of the same data) , a MAID can reduce data storage energy consumption by as much as 50 percent. That's good news for data centers, most of which are already at capacity, and increasingly legislated.:: Greener Computing :: Green Data Project