Performance and power issues are becoming increasingly important in the design of large, cluster-based multitier data centers for supporting a multitude of services. The design and analysis of such large/complex distributed systems often suffer from the lack of availability of an adequate physical infrastructure. This paper presents a comprehensive, flexible, and scalable simulation platform for in-depth analysis of multi-tier data centers. Designed as a pluggable three-level architecture, our simulator captures all the important design specifics of the underlying communication paradigm, kernel level scheduling artifacts, and the application level interactions among the tiers of a three-tier data center. The flexibility of the simulator is attributed to its ability in experimenting with different design alternatives in the three layers, and in analyzing both the performance and power consumption with realistic workloads. The scalability of the simulator is demonstrated with analyses of different data center configurations. In addition, we have designed a prototype three-tier data center on an Infiniband Architecture (IBA) connected Linux cluster to validate the simulator. Using RUBiS benchmark workload, it is shown that the simulator is quite accurate in estimating the throughput, response time, and power consumption. We then demonstrate the applicability of the simulator in conducting three different types of studies. First, we conduct a comparative analysis of the IBA and 10 Gigabit Ethernet (10GigE) under different traffic conditions and with varying size clusters for understanding their relative merits in designing cluster-based servers. Second, measurement and characterization of power consumption across the servers of a three-tier data center is done. Third, we perform a configuration analysis of the Web server (WS), Application Server (AS), and Database Server (DB) for performance optimization. We believe that such a comprehensive simulation infrastructure is critical for providing guidelines in designing efficient and cost-effective multi-tier data centers.