DCS: Diagonal Coding Scheme for Enhancing the Endurance of SSD-Based RAID Arrays

To guarantee high reliability, solid-state drive (SSD)-based storage systems require data redundancy schemes, e.g., redundant array of independent disks (RAID) schemes. Traditional RAID-5, RAID-6, and Reed-Solomon codes can tolerate one, two, and an arbitrary number of device failures, respectively. However, some SSDs under those redundant configurations may age much faster than others because of the high skewness and locality of workloads. The uneven aging rates may make some SSDs wear out very quickly and decrease the endurance of SSD-based RAID arrays. To address this problem, we first come up with a diagonal coding scheme (DCS) by distributing the updating dependencies evenly among devices to improve the system-level wear-leveling. DCS can efficiently improve the array endurance if requests are aligned with the stripe size, i.e., when data symbols in the same stripe receive the same number of writes, while the number could be different for different stripes. To relax the above assumption, we further propose an enhanced scheme, DCS+. With a buffer design, DCS+ can improve the wear-leveling among devices under general access patterns via triggering different responses to different kinds of requests. We conduct extensive trace-driven evaluations based on real-world workloads, and results show that our design efficiently enhances the endurance of SSD-based RAID arrays.