To meet ever increasing capacity and performance requirements of emerging data-intensive applications, highly distributed and multilayered back-end storage systems have been employed in large-scale high performance computing (HPC) environments. A main component of these storage infrastructures is the parallel file system (PFS), a especially designed file system for absorbing bulk data transfers from applications with thousands of concurrent processes. Load distribution on PFS data servers compose a major source of intra-application input/output (I/O) performance variability. Albeit mitigating variability is desirable, as it is known to harm application-perceived performance, understanding and dealing with I/O performance variability in such complex environments remains a challenging task. In this research, a differentiated approach for evaluating and mitigating intra-application I/O performance variability over PFSs is proposed. More specifically, from the evaluation perspective, a comprehensive approach combining complementary methods is proposed. An analytical model proposal, named DTSMaxLoad, provides estimates for the maximum load in a PFS data server. To complement DTSMaxLoad, modeling conditions and mechanisms hard to represent analytically, the Parallel I/O and Storage System (PIOSS) simulation model was proposed. Finally, for experimental evaluation over real environments, a flexible and distributed I/O performance evaluation tool, coined as IOR-Extended (IORE), was proposed. Furthermore, a high-level file distribution approach for PFSs, called N-N Round-Robin (N2R2), was proposed focusing on mitigating I/O performance variability for distributed applications where each process accesses an individual and independent file. An extensive experimental effort, including measurements on real environments, was conducted in this research work for evaluating each of the proposed approaches. In summary, this evaluation indicated both DTSMaxLoad and PIOSS modeling proposals can represent load distribution behavior on PFSs with significant fidelity. Moreover, results demonstrated N2R2 successfully reduced intra-application I/O performance variability for 270 distinct experimental scenarios, which, ultimately, translated into overall application I/O performance Improvements.
Flexibility and performance of parallel file systems
