Carl A. Waldspurger
To address these issues, we introduce PARDA, a novel software system that enforces proportional-share fairness among distributed hosts accessing a storage array, without assuming any support from the array itself. PARDA uses latency measurements to detect overload, and adjusts issue queue lengths to provide fairness, similar to aspects of flow control in FAST TCP. We present the design and implementation of PARDA in the context of VMware ESX Server, a hypervisor-based virtualization system, and show how it can be used to provide differential quality of service for unmodified virtual machines while maintaining high efficiency. We evaluate the effectiveness of our implementation using quantitative experiments, demonstrating that this approach is practical.