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Overview
========

SIONlib is a library for writing and reading binary data to/from
several thousands of processors into one or a small number of physical
files. For parallel access to files only the open and close functions
are collective while writing and reading file can be done
asynchronously. SIONlib provides a SIONlib file handle which
substitutes the C file pointer.

SIONlib provides a simplified file handling for parallel programs
which formerly read or write binary data in parallel into separate
files (task-local files). After opening the file with SIONlib, the I/O
can be done with the SIONlib equivalents to standard C-I/O
functionality (fwrite -> sion_fwrite, fread -> sion_fread) which have
the same syntax as their C counterparts. Instead of maintaining
thousands of separate files, there is only one large file containing
all data.

Given that each processor writes its data to same file, SIONlib
assigns different regions (e.g., data blocks) of the file to a
processor. Hence, for each processor, SIONlib needs the estimated (or
known) data size which will be written to the file (chunk
size). SIONlib can also handle extensions (additional chunks), if the
end of a data block is reached.

Both, the estimated chunk size and file system block size are used to
calculate the individual start position inside the file for each
processor. Ensuring contention-free access to file system blocks
enables efficient parallel writing and reading.

SIONlib is a joint project of
- [Forschungszentrum Jülich](http://www.fz-juelich.de/),
  [Jülich Supercomputing Centre (JSC)](http://www.fz-juelich.de/ias/jsc/)
- [German Research School for Simulation Sciences](http://www.grs-sim.de/)
- [Laboratory for Parallel Programming](https://www.parallel.informatik.tu-darmstadt.de/parallel-programming/)

Documentation
=============

- [List of all documentation](pages.html)
- [Download](http://www.fz-juelich.de/ias/jsc/EN/Expertise/Support/Software/SIONlib/sionlib-download_node.html)
- \ref installation_page
- \ref release_notes_page
- \ref api_page

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