A feedback-based model for I/O servicing

Modern I/O subsystems have increased their capacity and density but their performance has not been improved accordingly. To address this problem, we have developed a new model that is based on the feedback information provided to the I/O subsystem controller. The presented model is applied to a multiple disk drive subsystem, which serves requests in parallel. Under conventional servicing, each request refers to a speci®c drive and is placed on the corresponding disk drive queue in order to be serviced. The proposed feedback-based model redirects requests among disk drives towards performance gain. The feedback is evaluated by a metric identi®ed by the queue length per disk drive. Performance analysis proves that the feedback-based model results in e€ective and improved load distribution. The request servicing in a parallel disk drive subsystem is simulated and simulation runs measure both conventional and feedback-based servicing. The simulation results validate the presented model and prove that it shows an important improvement in both seek and servicing times compared with the conventional request servicing model.