About XIOS

XIOS is an '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. XIOS is Open Source software and licensed under the CeCILL license. Please see the license file in the software download for more details.

Advantages of using XIOS:

• 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 (the oifs_run command knows how to run OpenIFS with/without XIOS).
• XIOS is best suited to high resolution or climate length integrations. The added complexity of configuring XIOS makes it less suitable for medium/seasonal range.

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)