Main Page/PIO

This is the document page for parallel I/O library developed for NekCEM.

Background

File Format

Binary (used for production, compact size), or ASCII (used for debugging, human-readable)

Usage Introduction:

For traditional I/O approaches based on one file per processor, users can use #1,2,3 in .rea file for a specific example, by parameter 81.
These three approaches produce one file per processor and we will refer them as old libraries.

param(81) = 1: use nek5000 old_output format (ASCII, fld format) ---> xxx.fld.

param(81) = 2: use Fortran I/O library (ASCII, VTK format) ---> ascii-xxx.vtk.

param(81) = 3: use C-POSIX I/O libraries (binary, VTK format) ---> binary-xxx.vtk.

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Several advanced parallel I/O approaches were developed. Performance for those approaches are detailed in "Jing Fu et. al, Parallel I/O performance for application-level checkpointing on the Blue Gene/P" http://www.mcs.anl.gov/~mmin/ICS2011.pdf.

param(81) = 4: collective for N processors IO to 1 file ---> mpi-binary-N1-xxx.vtk

param(81) = 5: collective IO for N processors to multiple M-files ---> mpi-binary-NM-xxx.vtk.

param(81) = 6: reduced-blocking IO for N processors to 1 file with M writers ---> mpi-binary-NM1-xxx.vtk.

param(81) = 7: reduced-blocking IO for N processors to 1 file with M writers ---> mpi-ascii-NM1-xxx.vtk.

param(81) = 8: reduced-blocking IO for N processors to multiple M-files with M writers ---> mpi-binary-NMM-xxx.vtk.

Note that param(82) and param(83) need to be set correctly in *.rea file.

param(82) = number of output files,

param(83) = max number of fields to be written.

The output files with param(81)=2,3,4,5,6,7,8 cab be visualized with ParaView and VisIt.
The output with param(81)=1 can be visualized with nek5000 visualization tool, postx