An optimizer process in a storage system automatically selects access activity data for storage devices in the system during periods of interest so that a volume-swapping optimization analysis is based on desired device performance information and thus yields improved optimization results. For each of a number of sampling intervals in an analysis period, workload statistics are collected for logical volumes in the system. From the workload statistics, a service time is calculated for each storage device for each sampling interval. A set of highest service times is identified from the service times for each device, such as those above the 80th percentile, and a service time measure is generated from the set of highest service times. Devices having the highest and lowest measures are identified, and a pair of volumes is identified that, if swapped between the two devices, would improve the service time measure of the higher-service-time device without unduly degrading the service time measure of the lower-service-time device. Such volumes are subsequently swapped, improving the performance of the higher-service-time device and the overall system.