Prompt response to data access requests is the key performance concern of parallel storage systems. Sort partition (SP) is one of the most promising file allocation solutions for the static scenario due to its sorted partition and placing mechanism. The online variant of SP, hybrid partition (HP), however, does not perform well in the dynamic scenario. The recently proposed balanced allocation with sort (BAS) and its online version balanced allocation with sort for batch (BASB) try to compete with SP and HP by providing better load balancing together with sorting. BAS's performance is close to SP, and BASB greatly outperforms HP. In this paper, we proposed new file placement solutions for the parallel storage systems: Optimized Sort Partition (OSP) for the static scenario and Optimized Sort Partition Online (OSPOnline) for the dynamic scenario. By eliminating the drawbacks of SP/HP and BAS/BASB in the file assignment, OSP and OSPOnline can achieve optimized system response time. Conducted simulations show that OSP and OSPOnline steadily outperform their competitors under various conditions.