PERSES: Data Layout for Low Impact Failures

Growth in disk capacity continues to outpace advances in read speed and device reliability. This has led to storage systems spending increasing amounts of time in a degraded state while failed disks reconstruct. Users and applications that do not use the data on the failed or degraded drives are negligibly impacted by the failure, increasing the perceived performance of the system. We leverage this observation with PERSES, a statistical data allocation scheme to reduce the performance impact of reconstruction after disk failure. PERSES reduces degradation from the perspective of the user by clustering data on disks such that data with high probability of co-access is placed on the same device as often as possible. Trace-driven simulations show that, by laying out data with PERSES, we can reduce the perceived time lost due to failure over three years by up to 80% compared to arbitrary allocation.