parIO - parallel IO for Fortran MPI applications
--------------------------------------------
Parallel IO has to be robust, fast and still easy to use - this can become a difficult task, especially in highly parallel environments.
HDF5 (http://www.hdfgroup.org/HDF5) has proven to be the first choice for parallel IO in the last years. But it still is not a 'plug-and-play' solution if you are looking for best performance.
Without tuning it can easily slow down your IO compared with pure MPI-IO tremendously.

But the benefits of HDF5 over pure MPI-IO are huge: http://www.hdfgroup.org/why_hdf.
That´s why we wanted and had to stick with HDF5, even for our large computations with restart files > 2TByte each.
Therefore the wrapper library parIO was developed to keep the IO of our applications simple, while getting best read/write performance on different supercomputers.
It currently provides functionality to dump 1,2,3,4D arrays of different types, distributed over any number of MPI threads or not, as fast as possible to file
while keeping the details away from the application developer.

It is used in two different large scale applications of the ITV for production runs
on the supercomputers JUQUEEN (http://www.fz-juelich.de/ias/jsc/EN/Expertise/Supercomputers) at the Research Center Jülich
and the SuperMUC (http://www.lrz.de/services/compute/supermuc) at the Leibniz-Rechenzentrum.

Look at 'testIO/io/testio_io_basics.F90' to have an idea, how simple your IO routines will look like
for global values (e.g.):
            if(open_group(file_id, '/settings', group_id) ) then
                call r_gval(group_id, 'nhalt', nhalt, ierr)
                call r_gval(group_id, 'nstat', nstat, ierr)
                call close_group(group_id, ierr)
            end if

or for 1,2,3,4D arrays distributed over a large number of MPI threads

             memory:          file:
             ----------      -----------------------------
            |          |    |          ----------         |
            |   mem    | => |         |          |        |
            | [mdims]  |    |         |          |        |
             ----------     |         |          |        |
                            | _foffs-> ----------         |
                            |/                            |
                             -----------------------------
            if(open_group(file_id, '/flow', group_id)) then
                call r_pval(group_id, 'u', foffs, mdims, mem, ierr);
                call r_pval(group_id, 'v', foffs, mdims, mem, ierr)
                call r_pval(group_id, 'w', foffs, mdims, mem, ierr)
                call close_group(group_id, ierr)
            end if

             memory:                            file:
             -----------------------------      -----------------------------
            |                             |    |                             |
            |          ----------         |    |          ----------         |
            |         |          |        | => |         |          |        |
            |         |          |        |    |         |          |        |
            |         | [msize]  |        |    |         |          |        |
            | _moffs_> ----------         |    | _foffs-> ----------         |
            |/                    [mdims] |    |/                            |
             -----------------------------      -----------------------------
            if(open_group(file_id, '/flow', group_id)) then
                call r_pval(group_id, 'u', foffs, mdims, mem, msize, moffs, ierr);
                call r_pval(group_id, 'v', foffs, mdims, mem, msize, moffs, ierr)
                call r_pval(group_id, 'w', foffs, mdims, mem, msize, moffs, ierr)
                call close_group(group_id, ierr)
            end if

parIO will take care of:
------------------------
 - hide variable type and dimension specific functionality
 - different IO strategies (MPI-IO, POSIX, File-Splitting, direct-IO)
 - HDF5 specific settings and function (eg. buffer, padding, ...)
 - distribution of single array over multiple processors (hyperslab)
 - fast (compared with HDF5´s) precision conversion (e.g. read float from double), even for large datasets
 - currently supported data types: real4,real8,integer4,complex4,complex8 (0D,1D,2D,3D,4D)
 - simple setting attributes
 - error handling
 - dump tests
 - prints dump speed

requirements:
-------------
 Fortran 90/2003 compiler
 HDF5
  - http://www.hdfgroup.org/HDF5 (tested with 1.8.12)
  - check doc/configure_hdf5 for compilation hints
  - lots of third-party bindings (e.g. matlab, tecplot, paraview, visit, scilab, python, perl, etc.)
 sed
  - http://de.wikipedia.org/wiki/Sed_(Unix)
  - sed is used to generate source files for different variable types in src/interf from templates

license:
--------
  parIO is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as
  published by the Free Software Foundation and appearing in the
  file LICENSE.LGPL included in the packaging of this file;
  either version 3 of the license, or (at your option) any later version.

  Please review the following information to ensure the GNU Lesser
  General Public License version 3 requirements will be met:
  http://www.gnu.org/licenses/lgpl-3.0.txt

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU Lesser General Public License for more details.

contact:
--------
  Jens Henrik Göbbert
  Forschungszentrum Jülich GmbH
  Jülich Supercomputing Centre (JSC)
  <j.goebbert()fz-juelich.de>