We propose a storage cluster architecture CoStore, which evenly distributes system responsibilities across all collaborating cluster members without a separate central file manager. The serverless CoStore architecture has the potential to provide scalable high-performance high-capacity storage services with strong reliability and availability, traditionally only achievable by high-end storage systems.A prototype CoStore system has been implemented using cost-effective COTS-based network attached storage devices on commodity operating systems. The performance of the CoStore prototype has been measured and compared with those of other commonly available distributed file systems. Preliminary test results show that a single node CoStore has a comparable performance to that of NFS and that CoStore outperforms CIFS on Windows 2000.