Executive SummaryThe goal of Magellan, a project funded through the U.S. Department of Energy (DOE) Office of Advanced Scientific Computing Research (ASCR), was to investigate the potential role of cloud computing in addressing the computing needs for the DOE Office of Science (SC), particularly related to serving the needs of midrange computing and future data-intensive computing workloads. A set of research questions was formed to probe various aspects of cloud computing from performance, usability, and cost. To address these questions, a distributed testbed infrastructure was deployed at the Argonne Leadership Computing Facility (ALCF) and the National Energy Research Scientific Computing Center (NERSC). The testbed was designed to be flexible and capable enough to explore a variety of computing models and hardware design points in order to understand the impact for various scientific applications. During the project, the testbed also served as a valuable resource to application scientists. Applications from a diverse set of projects such as MG-RAST (a metagenomics analysis server), the Joint Genome Institute, the STAR experiment at the Relativistic Heavy Ion Collider, and the Laser Interferometer Gravitational Wave Observatory (LIGO), were used by the Magellan project for benchmarking within the cloud, but the project teams were also able to accomplish important production science utilizing the Magellan cloud resources.Cloud computing has garnered significant attention from both industry and research scientists as it has emerged as a potential model to address a broad array of computing needs and requirements such as custom software environments and increased utilization among others. Cloud services, both private and public, have demonstrated the ability to provide a scalable set of services that can be easily and cost-effectively utilized to tackle various enterprise and web workloads. These benefits are a direct result of the definition of cloud computing: on-demand self-service resources that are pooled, can be accessed via a network, and can be elastically adjusted by the user. The pooling of resources across a large user base enables economies of scale, while the ability to easily provision and elastically expand the resources provides flexible capabilities.Following the Executive Summary we summarize the key findings and recommendations of the project. Greater detail is provided in the body of the report. Here we briefly summarize some of the high-level findings from the study.• Cloud approaches provide many advantages, including customized environments that enable users to bring their own software stack and try out new computing environments without significant administration overhead, the ability to quickly surge resources to address larger problems, and the advantages that come from increased economies of scale. Virtualization is the primary strategy of providing these capabilities. Our experience working with application scientists using the cloud demonstrated the power of virtualization to enable ...