“…This multi-layered structure of the Grid suggests that the observed performance of Grid services and applications is affected by a variety of factors, such as [27]: (i) the performance capacity of local Grid sites (this depends on the performance of hardware entities, such as CPUs, memory hierarchies, computing nodes, storage devices, local networking, and clusters); (ii) the performance of the wide-area networks connecting Grid sites into a Grid infrastructure; (iii) the performance and overhead of libraries and services providing Grid applications with support for communication, synchronization, bulk data transfer, database querying, and other higher-level Grid programming abstractions; (iv) the performance and overhead of Grid services supporting job submission and management, such as workload management systems, resource brokers, and Grid information services; and (v) the reliability and the robustness of Grid middleware and services.…”