Storage clusters use a lot of energy, so devising a power efficiency scheme to conserve energy is worthwhile. The authors of this paper caution that while existing energy conservation techniques for storage clusters reduce energy consumption, the savings come at the expense of reduced performance or reliability of the systems. The paper describes an approach that overcomes most of the negative aspects while improving the energy efficiency of the storage cluster by what the authors claim is almost 30 percent over similar but energy-oblivious storage implementations.

The authors describe the application of their approach to erasure-coded storage clusters. Erasure coding is a method of data protection that improves the ability to recover data from storage node failures. They apply a mathematical function to take data fragments and expand them in an efficient manner that requires less redundancy for a high level of recoverability (relative to more commonly used techniques). Those data pieces are then spread across storage nodes.

The proposed strategy requires the management of storage nodes so that as many components of the storage nodes as possible are kept in low-power mode. One method of doing this is to defer updates (in other words, use buffered writes) to nonvolatile random access memory (NVRAM) or flash devices on a temporary basis, which avoids having to spin up disks that are in the low-power mode.

The paper goes into a lot of technical detail on how the proposed strategy works. Storage system designers should find it useful.