中文摘要：

随机Petri网（SPN）是一种灵活有力的建模工具，在可信赖性研究方面已形成较为成熟的理论体系。采用SPN网对机群系统前端分配器及后端服务器进行建模，通过在系统建模时对前端分配器给予必要的修复保证，给出整个机群系统的SPN模型，在模型分析的基础上给出了机群系统的可信赖性参数，并对模型进行了仿真分析。仿真结果表明，在对关键系统前端分配器给予修复保证后，系统模型的稳态可用性将大大提高。

英文摘要：

Stochastic Petri nets （SPN） is a kind of flexible modeling tool. The theory system on the research of dependability is well established. The author takes advantage of SPN to model front-end dispatcher and backend workers respectively, and SPN model of the whole cluster system is presented. It has taken the repairing assurance into consideration when model cluster system. Different dependable parameters of the cluster system based on model analysis is presented, and the model is simulated. The simulation results show that the availability of system model will increase largely after the critical system front-end dispatcher is given repairing assurance enough.