MPIIO

MPIIO, commonly written as MPI-IO, is the parallel input/output interface of the Message Passing Interface (MPI) standard. It provides a portable API for high-performance file operations in parallel applications, allowing many processes to read and write a single shared file concurrently while abstracting details of the underlying file system and hardware.

Core concepts include an MPI_File handle that represents an open file and the notion of a file view defined with MPI_File_set_view. The view describes how data in memory maps to the file, using MPI datatypes to describe complex, potentially noncontiguous layouts. MPI-IO supports both independent and collective I/O routines, noncontiguous access patterns, and advanced features such as data sieving and two-phase I/O to improve throughput and overlap computation with I/O.

Portability and implementations: MPI-IO is part of MPI-2 and is extended in subsequent revisions. It is implemented in major MPI distributions such as MPICH, Open MPI, and Intel MPI. It works with a variety of parallel file systems, including Lustre, GPFS, PVFS, and NFS, enabling optimizations that utilize file system capabilities.

Usage with higher-level libraries: many scientific formats, such as HDF5 and NetCDF, rely on MPI-IO to provide parallel I/O. MPI-IO can be used directly for custom I/O patterns and underlying these libraries to achieve scalable performance for large datasets.

History and scope: MPI-IO originated in the MPI-2 standard with continued evolution in later MPI specifications. It remains a foundational mechanism for parallel I/O in high-performance computing, offering portable semantics and opportunities for optimized access patterns.