The design and performance evaluation of the RAID 5 controller using the load-balanced destage algorithm

Write requests are written from the disk cache to the disks by the destage algorithm, and the response time of host read request dominates the performance of the disk. Since RAID is composed of multiple disks, although the performance at the disk level is important to service requests, effectively the performance at the disk array level is more important. In RAID, a host request cannot be completed until all the striped requests are completed and the response time of the host request is dependent on the response time of the disk with the heaviest load. However, existing destage algorithms do not take into consideration the overall performance of all disks in the RAID but destage write requests for optimal performance at each individual disk, and it may eventually lead to overload of a few disks. It may delay the service of some striped requests, and therefore, the response time of host request increases. The paper suggests a novel Load-Balanced Destage (LBD) algorithm adopted at the disk array level, and shows that the LBD algorithm has a higher performance than existing destage algorithms by evaluating their performance using a simulator.