WeLe-RAID: A SSD-Based RAID for System Endurance and Performance

Due to the limited erasure/program cycles of flash memory, flashbased SSDs need to prolong their life time using wear-leveling mechanism to meet their advertised capacity all the time. However, there is no wear-leveling mechanism among SSDs in RAID system, which makes some SSDs wear out faster than others. Once any one of SSDs fails, reconstruction must be triggered immediately. But, the cost of this process is so high that the reliability and availability is affected seriously. We propose WeLe-RAID which introduces Wear-Leveling mechanism among flash SSDs to enhance the endurance of entire SSD-based RAID system. As we know that under the workload of random access pattern, parity stripes suffer from much more updates because every update to the data stripe would cause the modification to the related parity stripe. Based on this principle, we introduce age-driven parity distribution scheme to guarantee the wear-leveling among flash SSDs. At the same time, because of age-driven parity distribution, it brings into the performance benefit with better load balance. Compared with conventional RAID mechanism, it significantly improves the life span and performance with ignorable overhead.