Disk Subsystem Performance Evaluation: From Disk Drives to Storage Area Networks

Disk subsystems span the range of configuration complexity from single disk drives to large installations of disk arrays. They can be directly attached to individual computer systems or configured as larger, shared access Storage Area Networks (SANs). It is a significant task to evaluate the performance of these subsystems especially when considering the range of performance requirements of any particular installation and application. Storage subsystems can be designed to meet different performance criteria such as bandwidth, transactions per second, latency, capacity, connectivity, ...etc. but the question of how the subsystem will perform depends on the software and hardware layering and the number of layers an I/O request must traverse in order to perform the actual operation. As an I/O request traverses more and more software and hardware layers, alignment and request size fragmentation can result in performance anomalies that can degrade the overall bandwidth and transaction rates. Layer traversal can have a significant negative impact on the observed performance of even the fastest hardware components. This paper walks through the Storage Subsystem Hierarchy, defining these layers, presents a method for testing in single and multiple computer environments, and demonstrates the significance of careful, in-depth evaluation of Storage Subsystem Performance.