We present an auto-tuning system for optimizing I/O performance of HDF5 applications and demonstrate its value across platforms, applications, and at scale. The system uses a genetic algorithm to search a large space of tunable parameters and to identify effective settings at all layers of the parallel I/O stack. The parameter settings are applied transparently by the auto-tuning system via dynamically intercepted HDF5 calls.To validate our auto-tuning system, we applied it to three I/O benchmarks (VPIC, VORPAL, and GCRM) that replicate the I/O activity of their respective applications. We tested the system with different weak-scaling configurations (128, 2048, and 4096 CPU cores) that generate 30 GB to 1 TB of data, and executed these configurations on diverse HPC platforms (Cray XE6, IBM BG/P, and Dell Cluster). In all cases, the auto-tuning framework identified tunable parameters that substantially improved write performance over default system settings. We consistently demonstrate I/O write speedups between 2x and 100x for test configurations.

We examine the I/O behavior of thousands of supercomputing applications "in the wild," by analyzing the Darshan logs of over a million jobs representing a combined total of six years of I/O behavior across three leading high-performance computing platforms. We mined these logs to analyze the I/O behavior of applications across all their runs on a platform; the evolution of an application's I/O behavior across time, and across platforms; and the I/O behavior of a platform's entire workload. Our analysis techniques can help developers and platform owners improve I/O performance and I/O system utilization, by quickly identifying underperforming applications and offering early intervention to save system resources. We summarize our observations regarding how jobs perform I/O and the throughput they attain in practice.

Accurate analysis of HPC storage system designs is contingent on the use of I/O workloads that are truly representative of expected use. However, I/O analyses are generally bound to specific workload modeling techniques such as synthetic benchmarks or trace replay mechanisms, despite the fact that no single workload modeling technique is appropriate for all use cases. In this work, we present the design of IOWA, a novel I/O workload abstraction that allows arbitrary workload consumer components to obtain I/O workloads from a range of diverse input sources. Thus, researchers can choose specific I/O workload generators based on the resources they have available and the type of evaluation they wish to perform. As part of this research, we also outline the design of three distinct workload generation methods, based on I/O traces, synthetic I/O kernels, and I/O characterizations. We analyze and contrast each of these workload generation techniques in the context of storage system simulation models as well as production storage system measurements. We found that each generator mechanism offers varying levels of accuracy, flexibility, and breadth of use that should be considered before performing I/O analyses. We also recommend a set of best practices for HPC I/O workload modeling based on challenges that we encountered while performing our evaluation.

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