Abstract: Previous work on performance evaluation of networked storage systems has been mostly qualitative, and the quantitative analytical method and model are still limited. A quantitative analytical model based on CQN-FC (closed queueing networks with finite capacity) is presented according to the data flow of distributed networked software RAID (dns-RAID). In order to cope with the state space explosion problem of CQN-FC solution, a novel approximate performance bounds analysis (APBA) method is proposed, which has lower computational complexity than other approximate analytical methods in the literature. Experimental testing results show that, the performance bounds of dns-RAID based on CQN-FC calculated by APBA method can reflect the actual throughput and I/O response time bounds in light load, heavy load and over load respectively, and can offer the maximal system load as well.