Energy Conservation of RAID by Exploiting SSD Cache

Energy conservation of server systems has become important. Though storage subsystem is one of the biggest power consumers, development of energy conservation techniques is challenging problem due to striping techniques like RAID and physical characteristics of hard disks. According to our observation, the size of footprint for a day or for hours is much smaller compared to the size of whole data set. In this paper, we describe a design of a novel architecture for RAID that uses an SSD as a large cache to conserve energy by holding such a footprint. We incorporate these approaches into a real implementation of a RAID 5 system that consists of four hard disks and an SSD in a Linux environment. Our preliminary results in actual performance measurements using the cello99 and SPC traces show that energy consumption is reduced by a maximum of 14%.