Dual RAID: A scheme for high reliable all flash array

Flash-based solid state disks (SSDs) are replacing hard disk drives owing to its high performance and low energy consumption. For both high reliability and large capacity, redundant array of independent disks (RAID) is commonly used in storage system. In all flash arrays, the HDDs in RAID are substituted by SSDs and it gains improvements in bandwidth and IOPS (Input/output Operations per Second) by leaps and bounds owing to SSDs high performance. However, the error mode of SSD is different from HDD. The uncorrectable page errors in SSD are a great threat especially when a disk fails. For high reliability, we proposed a Dual-RAID scheme to protect data at disk level and block level respectively. To correct the disk failure, the proposed scheme adopts RAID-5 between disks. For recovering uncorrectable page errors, a redundant array of independent NANDs (RAIN) scheme is applied to SSD by exploiting its multi-channel structure. Although the redundancy overhead of the proposed scheme is about the same as RAID-6, the dual-RAID scheme achieves better performance and higher reliability. The experiment shows that the proposed scheme improves performance 35% on totally random trace in comparison to RAID 6 scheme.