Augmenting RAID with an SSD for Energy Relief

In this paper, we describe a design of a novel architecture for RAID that uses an SSD as a large cache to conserve energy. This approach stems from the fact that short term footprints are small enough to be efficiently managed within an SSD. More specifically, in this study, we consider two simple approaches to reduce the energy consumed in RAID. First, when a read happens in RAID, a copy of the read request is copied to the SSD, so that future requests may be serviced by the SSD. Then, for writes, all writes are buffered in SSDs so that the interval between requests may be increased reducing activities at RAID disks. 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%.