The parity calculation technique of the RAID5 provides high reliability, efficient disk space usage, and good read performance for parallel-disk-array configurations. However, it requires four disk accesses for each write request. The write performance of a RAID5 is therefore poor compared with its read performance. In this paper, we propose a buffering system to improve write performance while maintaining the reliability of the total system. The buffering system uses two to four disks clustered into two groups, primary and backup. Write performance is improved by sequential accesses of the primary disks without interruption and by reduction of irrelevant disk accesses for the RAID5 by packing. The backup disks are used to tolerate a disk failure and to accept read requests for data stored in the buffering system so as not to disturb sequential accesses in the primary disks. We developed an experimental system using an off-the-shelf personal computer and disks, and a commercial RAID5 system. The experiments indicate that the buffering system considerably improves both system throughput and average response time.