Reliability-aware energy management for hybrid storage systems

Abstract

Modern disk-based storage systems are not energy proportional, because disks consume almost as much power when idle (but spinning) as they do when actively accessing data. We combine a power-aware, solid-state (flash) cache and a reliability-aware disk spin-down mechanism to significantly improve storage energy proportionality without hurting disk reliability, data integrity, or performance. We evaluated the resulting power- and reliability-aware hybrid flash-disk RAID storage array and found that it reduces energy consumption by 85% compared to a similar-cost, similar-performance typical configuration of all SAS drives that are never spun down. Our design also achieves almost 50% energy savings compared to hybrid flash-disk systems tuned for performance or that do not take full advantage of opportunities for safe spin-down. Further, unlike most previous work that exploits spindown to save energy, we limit the rate at which disks are spun down to avoid premature mechanical failures, whereas reliability-unaware spindown algorithms can exceed manufacturer waranteed lifetime spindown limits in as little as one year. © 2011 IEEE.