Abstract: The parallel I/O system is one of important components of a HPC system，and it can discount the performance of the whole system if its availability are awful.However，high-throughput and large capacity are still the main target in parallel I/O system’s design by far，and few research on its availability evaluation has been published.In this paper，a method managing to evaluate a parallel I/O system’s availability based on SANs（Stochastic Activity Networks） model with Mobius modeling environment is expatiated，and the simulation results reveal how the availability of the parallel I/O system is impacted on by the number of global file system，the number of minimum number of OST in a single file system，and the repair period of the whole system.

Key words: Stochastic Activity Networks（SANs）, Mobius, parallel I/O system, availability evaluation

摘要： 并行I/O系统是高性能计算机系统的一个重要组成部分，其可用性水平对整机系统性能的发挥具有重要作用。采用SANs（Stochastic Activity Networks，随机行为网）模型及其支持工具Mobius，对一种大规模并行I/O系统建立可用性评估模型，并采用模拟方法进行解析。模拟结果反映了全局文件系统数量、单一文件系统内最小可用OST（Object Storage Target，对象存储目标）数量和系统维修时间等参数的变化对全系统可用度的影响，对于大规模并行I/O系统的设计与维护具有积极的参考价值。

关键词: 随机行为网, Mobius, 并行I/O系统, 可用性评估