Rimac

Energy efficiency becomes increasingly important in today's high-performance storage systems. It can be challenging to save energy and improve performance at the same time in conventional (i.e. single-rotation-rate) disk-based storage systems. Most existing solutions compromise performance for energy conservation. In this paper, we propose a redundancy-based, two-level I/O cache architecture called RIMAC to address this problem. The idea of RIMAC is to enable data on the standby disk to be recovered by accessing data in the two-level I/O cache or on currently active/idle disks. At both cache and disk levels, RIMAC dynamically transforms accesses toward standby disks by exploiting parity redundancy in parity-based redundant disk arrays. Because I/O requests that require physical accesses on standby disks involve long waiting time and high power consumption for disk spin-up (tens of seconds for SCSI disks), transforming those requests to accesses in a two-level, collaborative I/O cache or on active disks can significantly improve both energy efficiency and performance.In RIMAC, we developed i) two power-aware read request transformation schemes called Transformable Read in Cache (TRC) and Transformable Read on Disk (TRD), ii) a power-aware write request transformation policy for parity update and iii) a second-chance parity cache replacement algorithm to improve request transformation rate. We evaluated RIMAC by augmenting a validated storage system simulator, disksim. For several real-life server traces including HP's cello 99, TPC-D and SPC's search engine, RIMAC is shown to reduce energy consumption by up to 33% and simultaneously improve the average response time by up to 30%.