The main problem we address in this paper is how to map the requirements of a known media service workload into the corresponding system resource requirements and to accurately size the required system. In this paper, we propose a new capacity planning framework for evaluating the resources needed for processing a given streaming media workload with speci ed performance requirements. In our tool, the service provider speci es the desirable system performance by stating two types of requirements in a Service Level Agreement (SLA): i) basic capacity requirements that de ne the percentage of time the con guration is capable of processing the workload without performance degradation while satisfying the speci ed system utilization and ii) performability requirements that de ne the acceptable degradation of service performance during the remaining, non-compliant time and in case of node failures. Using a set of specially benchmarked media server con gurations, the capacity planning tool mat...