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Process replication is provided as the central mechanism for application level software fault tolerance in SwiFT and DOORS. These technologies, implemented as reusable software modules, support cold and warm schemes of passive replication. The choice of a scheme for a particular application is based on its availability and performance requirements. In this paper we analyze the performability of a server software which may potentially use these technologies. We derive closed form formulae for availability throughput and probability of loss of a job. Six scenarios of loss are modeled and for each, these expressions are derived. The formulae can be used either of time or online to determine the optimal replication scheme.