This paper presents the Markov model for the reliability analysis of a linear consecutive 2-out-of-4 repairable system operating with the help of a linear consecutive 2-out-of-4 external supporting device. The system is analyzed using first order linear differential equation to develop the explicit expression for steady-state availability, busy period and profit function. Based on assumed numerical values given to system parameters, graphical illustrations are given to highlight important results. In addition, the effect of failure and repair on availability and profit are researched.

Reliability is a performance factor applied to multi-computer network system consisting of devices such as active parallel or redundant hosts (clients), distributed database servers with replication, anda central server. For reliability evaluation and performance of such a system, this study analyzed a computer network system consisting of hosts (clients) connected to two distributed database servers in replication to each other. The system is configured as a series-parallel system consisting of two subsystems, namely A and B. Subsystem A consists of three clients in active parallel while subsystem B consists od two distributed database servers in replication to each order. Both clients and server failure and repair time are to be exponentially distributed The system is analyzed using first-order differential-difference equations to derive the expressions for the availability, mean time to failure, probability of a busy period of repairman due to partial or complete failure. The results are presented in tables and graphs. Reliability characteristics such as availability, MTTF, profit function as well as sensitivity analysis have been discussed. The computed results are demonstrated by tables and graphs. From the analysis of reliability characteristics, it is evident that availability, profit , and mean time to failure can be enhanced by adding more servers in replication to each other.