The NERSC staff continues to provide our user community with highly rated support services and with an unmatched availability of computing resources. Every year, an annual survey of users shows that the quality of services provided by NERSC gets better and better. In addition to this survey, NERSC has also established a series of related goals and annually assess our performance against them to ensure that our staff remains focused on meeting the needs of NERSC and advancing computational science in supporting DOE's mission areas. This report, the fifth in a series, describes how the NERSC staff is working to achieve these goals and the overall objective of providing unparalleled systems and services to the scientific community.

This fourth annual self-assessment of the systems and services provided by the U.S. Department of Energy's National Energy Research Scientific Computing Center describes the efforts of the NERSC staff to support advanced computing for scientific discovery. Our staff applies experience and expertise to provide world-class systems and unparalleled services for NERSC users. At the same time, members of our organization are leading contributors to advancing the field of high-performance computing through conference presentations, published papers, collaborations with scientific researchers and through regular meetings with members of similar institutions. We believe that, by any measure, the results of our efforts underscore NERSC's position as a global leader in scientific computing.

The scale of Leadership Class Systems presents unique challenges to the features and performance of operating system services. This paper reports results of comprehensive evaluations of two Light Weight Operating Systems (LWOS), Cray's Catamount Virtual Node (CVN) and Linux Environment (CLE) operating systems, on the exact same large-scale hardware. The evaluation was carried out over a 5-month period on NERSC's 19,480 core Cray XT-4, Franklin, using a comprehensive evaluation method that spans Performance, Effectiveness, Reliability, Consistency and Usability criteria for all major subsystems and features. The paper presents the results of the comparison between CVN and CLE, evaluates their relative strengths, and reports observations regarding the world's largest Cray XT-4 as well.

This is the sixth self-assessment of the systems and services provided by the U.S. Department of Energy's National Energy Research Scientific Computing Center, describing many of the efforts of the NERSC staff to support advanced computing for scientific discovery. The report is organized along the 10 goals set by our staff and outlines how we are working to meet those goals. Our staff applies experience and expertise to provide world-class systems and unparalleled services for NERSC users. At the same time, members of our organization are leading contributors to advancing the field of high-performance computing through conference presentations, published papers, collaborations with scientific researchers and through regular meetings with members of similar institutions. In the fast-moving realm of high-performance computing, adopting the latest technology while reliably delivering critical resources can be a challenge, but we believe that this self-assessment demonstrates that NERSC continues to excel on both counts.