GRAID: A Green RAID Storage Architecture with Improved Energy Efficiency and Reliability

Existing power-aware optimization schemes for disk-array systems tend to strike a delicate balance between energy consumption and performance while ignoring reliability. To achieve a reasonably good trade-off among these three important design objectives in this paper we introduce an energy efficient disk array architecture, called a Green RAID (or GRAID), which extends the data mirroring redundancy of RAID 10 by incorporating a dedicated log disk. The goal of GRAID is to significantly improve energy efficiency or reliability of existing RAID-based systems without noticeably sacrificing their reliability or energy efficiency. The main idea behind GRAID is to update the mirroring disks only periodically while storing all updates since the last mirror-disk update in a log disk, thus being able to spin down all the mirroring disks (or half of the total disks) most of the time to a lower power mode to save energy without sacrificing reliability. Reliability analysis shows that the reliability of GRAID, in terms of MTTDL (Mean Time To Data Loss), is only slightly worse than RAID 10. On the other hand, our prototype implementation of GRAID and performance evaluation show that GRAID's energy efficiency is significantly better than that of RAID 10 by up to 32.1% and an average of 25.4%.