The RAID5 provides high reliability and efficient disk utilization. However, its performance for small writes is not enough high compared with its read performance, because a small write for a RAID5 requires four disk accesses. In this paper, we evaluate the performance of Fault-tolerant Buffering Disks (FBD) for improving the write performance of RAID5 with keeping the reliability. The FBD uses a few disks for buffering data without any modifications in disk arrays. The buffering disks are classified into primaries and backups. The primary disks enhance the write performance by continuous accesses that minimize head seek time and rotation latency, and by packing mechanism that removes redundant accesses. Backup disks keep copies to accept read requests while providing fault-tolerance. We have implemented an experimental FBD system using an off-the-shelf PC, and evaluated its throughput and response time under various environment with a commercial RAID5 system.
Transactions of IEICE D-I, Vol.J84-D-I, No.6, IEICE, 2001.6.