Abstract: An expandable, low price per storage unit, distributed RAID storage cluster system is presented to substitute the traditional hardware RAID array. It has three important features. First, it's a P2P infrastructure via network share storage model, with each data node in a completely equal status, and provides a great convenience in the expandability of distributed RAID system. Secondly, it sustains single I/O space(SIOS)feature by synchronizing RAID operations in user space, which is independent of the kernel-level RAID implementation, thus can support various advanced RAID technologies. Thirdly, it provides a virtual block device access interface, transparent to upper level file system and database system, thus can be directly used by application without any changes. Also, the system provides a node failure detection and recovery mechanism, which can effectively detect and replace failure nodes to guarantee data integrity and maintain system reliability. Experiments show that network shared storage model brings little impact on storage access bandwidth and the maximal sequential read bandwidth can reach 190 MBps, which is limited by the bandwidth of gigabit Ethernet. Also, experiments validate the reliability of the distributed RAID system. Under RAID6 configuration, one or two nodes failure will not interrupt data service, but one node failure leads to 15% bandwidth decline and two nodes failure leads to 18% bandwidth decline.