The grid computing vision promises to provide the needed platform for a new and more demanding range of applications. For this promise to become true, a number of hurdles, including the design and deployment of adequate resource management and information services, need to be overcome. In this context, understanding the characteristics of real grid workloads is a crucial step for improving the quality of existing grid services, and in guiding the design of new solutions. Towards this goal, in this work we present the characteristics of traces of four real grid environments, namely LCG, Grid3, and TeraGrid, which are among the largest production grids currently deployed, and the DAS, which is a research grid. We focus our analysis on virtual...