Flash-Aware RAID Techniques for Dependable and High-Performance Flash Memory SSD

Solid-state disks (SSDs), which are composed of multiple NAND flash chips, are replacing hard disk drives (HDDs) in the mass storage market. The performances of SSDs are increasing due to the exploitation of parallel I/O architectures. However, reliability remains as a critical issue when designing a large-scale flash storage. For both high performance and reliability, Redundant Arrays of Inexpensive Disks (RAID) storage architecture is essential to flash memory SSD. However, the parity handling overhead for reliable storage is significant. We propose a novel RAID technique for flash memory SSD for reducing the parity updating cost. To reduce the number of write operations for the parity updates, the proposed scheme delays the parity update which must accompany each data write in the original RAID technique. In addition, by exploiting the characteristics of flash memory, the proposed scheme uses the partial parity technique to reduce the number of read operations required to calculate a parity. We evaluated the performance improvements using a RAID-5 SSD simulator. The proposed techniques improved the performance of the RAID-5 SSD by 47 percent and 38 percent on average in comparison to the original RAID-5 technique and the previous delayed parity updating technique, respectively.