Abstract
This article investigates the influence of some system parameters on a system consisting of a 2-unit cold standby system with a single repair person. The system failure is due to an external factor like Poisson shocks that occur in different times. The shocks arrive according to a Poisson process, in addition to the fact that its magnitudes are independent random variable that follows a known distribution. The measures of reliability are determined by using a supplementary variable technique and Laplace transform. The sensitivity and relative sensitivity analysis of the reliability characteristics in terms of the system parameters are calculated. There is also a comparison between two-stage Erlang and exponential distribution as a special case.