Abstract: As an important component of Dawning 3000 super server, the COSMOS cluster file system allows to explore many important fields in the cluster file system, including architecture, protocol and performance optimization. Described in this paper is the implementation of the COSMOS cluster file system based on BCL 3 high speed communication protocol in Dawning 3000 cluster. Then parallel bandwidth utilization is introduced to describe the influence of communication and I/O subsystem on the performance of the cluster file system. Finally, the related experiments are reported and explained.