Performance is usually measured in terms of the value in completing tasks on time.
Reliability is evaluated by hardware and software failure models.
In many situations, there are trade-offs between task performance and task reliability. Assuming that the reliability of task execution is achieved through task replication, we present an approach that mathematically determines the replication factor for tasks. Our approach is novel in that it is a task schedule based analysis rather than a state based analysis as found in other models. In this work, the goal is to maximize the total performance index, which is a performance-related reliability measurement. We present a technique based on a continuous task model and show how it very closely approximates discrete models and tasks with varying characteristics.