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

Users can use #1,2,3,4,5,6,7,8 in .rea file for a specific example, by parameter 81.

Several advanced parallel I/O approaches based on MPI-IO library 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 [1] Recommended formats for parallel runs are param(81)=4 or 6. (or 7 if ASCII is preferred).

 proc=processors
 param(81) = 4: collective IO for N proc to 1 file ---> mpi-binary-N1-xxx.vtk 
 param(81) = 5: collective IO for N proc to multiple M-files ---> mpi-binary-NM-xxx.vtk
 param(81) = 6: reduced-blocking IO for N proc to 1 file with M writers ---> mpi-binary-NM1-xxx.vtk
 param(81) = 7: reduced-blocking IO for N proc to 1 file with M writers ---> mpi-ascii-NM1-xxx.vtk
 param(81) = 8: reduced-blocking IO for N proc to multiple M-files with M writers ---> mpi-binary-NMM-xxx.vtk

Recommended formats for parallel runs are param(81)=4 or 6. (or 7 if ASCII is preferred).

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

For traditional I/O approaches based on one file per processor, using old libraries, one can use

 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 

 param(81) = 1: use nek5000's old output format (ASCII) -> xxx.fld

Visualization

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