The carousel storage system is an automated warehousing system which has been widely used in a broad range of applications. This paper examines the effects of storage assignment policy on the throughput performance of the carousel system in which a storage/retrieval machine performs pickup/discharge operations. For 2-class-based storage assignment policy, the expected cycle time models are developed for single and dual command cycles. It is shown that with 2-class-based storage assignment policy significant reductions in cycle time are obtainable over randomized storage assignment policy. The effects of the system parameters such as the skewness of the inventory distribution, the shape factor and the pickup/discharge time are studied on the optimal boundary.