Abstract: In this paper we present a M/G/1 queueing model of Redundant Arrays of Inexpensive Disks （RAIDs） by means of Queueing Theory.Based on the model,we analyse some important performance parameters of RAIDs,such as average response time of I/O requests,sustained data transfer rates,and compare the differences between synchronized an asynchronized RAIDs.Finally,we propose THROUGHPUT as an overall parameter to evaluate the RAIDs’performance,and give proof of the theorem to determine the maximum throughput.