To meet the increasing demands of parallel scientific applications, supercomputers continue to grow in both scale and complexity. The fastest supercomputer in the world, El Capitan, features over a million CPU cores and tens of thousands of GPUs. Applications running on such large-scale systems are particularly susceptible to system noise or interference caused by the operating system (OS) and other services running on the same compute nodes as the application.

Effectively using I/O resources on HPC machines is a black art. The purpose of this tutorial is to shed light on the state-of-the-art in parallel I/O and to provide the knowledge necessary for attendees to best leverage the I/O resources available to them. We cover the entire I/O software stack from parallel file systems at the lowest layer, to intermediate layers (such as MPI-IO), and finally high-level I/O libraries (such as HDF-5). The emphasis is not just on how to use these layers, but ways to use them that result in high performance.This tutorial first discusses parallel file systems (PFSs). We cover general concepts and examine three examples: GPFS, Lustre, and PVFS2. Next we examine the upper layers of the I/O stack, covering four interfaces: POSIX I/O, MPI-IO, Parallel netCDF, and HDF5. We discuss interface features, show code examples, and describe how application calls translate into PFS operations.