What is XIOS?

XIOS is a 'I/O server' that can run alongside OpenIFS and handle all of the output from the model (apart from log files). The XIOS home page is: https://forge.ipsl.jussieu.fr/ioserver

It offers the following advantages:

• XIOS outputs netCDF4 and can be configured to interpolate to a regular lat-lon grid.
• XIOS can do computation of averages (e.g. in time) before output.
• XIOS makes openifs execute more efficiently as it executes in parallel.

XIOS is particularly well suited to running OpenIFS at higher resolutions as it removes the time required for OpenIFS to produce output. OpenIFS without XIOS can only write its GRIB output through the master process, typically around 5-10% penalty.

Disadvantages of using XIOS are:

• XML files are required to describe the netCDF output required.
• Batch jobs (if used) might be more complex as two separate MPI executables are required.

In this guide

This guide explains how to build and use XIOS with OpenIFS.

Prerequisites

XIOS requires other libraries are available before compilation. They are:

• netCDF4 library (either serial or netcdf parallel library)
• HDF5 library
• C++ compiler
• Fortran compiler - a recent version is recommended as XIOS uses some F2008 features (arrays > 7 dimensions)

Compiling & installing XIOS

This section walks through an install of XIOS suitable for use with OpenIFS.  Also see the XIOS webpages for more details.

XIOS uses a custom way of building & installing. The following examples will likely need adapting for your own environment but should provide a good guideline.

Download XIOS-2.5

XOS exists in a subversion repository. To download the latest version (version 2.5) at time of writing, do:

svn co http://forge.ipsl.jussieu.fr/ioserver/svn/XIOS/branchs/xios-2.5   xios-2.5
cd xios-2.5

n.b. the spelling of 'branchs' is correct!

Setup compilation environment

The next step is the setup the correct compilation environment. XIOS uses a couple of files for this purpose.