Performance of Redundant Disk Array Organizations in Transaction Processing Environments

We study the performance of two redun dant disk array organizations in a transaction processing environment and compare it to that of mirrored disk organi zations and organizations using no striping and no redun dancy. Redundant disk arrays and mirrored disks are used for providing rapid recovery from mediafailures in systems requiring high availability. The disk array organizations examined are: data striping with rotated parity (RAIDS) and Parity Striping. RAIDS provides high data transfer rates by striping the data over multiple disks. It also pro vides better load balancing over the disks in the array. At the same time, data striping increases disk arm use which can lead to longer queuing delays. In transaction process ing environments, because of the nature of I/O requests, namely a large number of small size requests, disk arms are a more valuable resource than data transfer bandwidth. Hence, parity striping was proposed as an alternative to RAIDS. It provides rapid recovery from failure at the same low storage cost without interleaving the data over multiple disks. In this study, we use data from a large scale commer cial transaction processing site to evaluate and compare the performance of the above organizations. We consider both non-cached systems as well as systems using a non-volatile cache in the controller.