XIOS is an HPC library dedicated to data flow management for ESM models. It provides a flexible and efficient way to read or write data on parallel file systems using asynchronous parallel I/O server technology. XIOS also provides powerful online data processing before output such as time integration, combination with arithmetic operators, vertical and horizontal interpolation, remapping (including 2nd order conservative), reduction operations, etc.

To output CMIP6 data, CNRM and IPSL experienced the same workflow based on XIOS in order to produce data suitable to publication requirements. The costly and traditional post-processing phase is now performed "In Situ" at run time and in a parallel way on the whole computing nodes, before to be written to the parallel filesystem through the I/O servers technology. In the talk, we will describe the different steps of this work, as a practical case study.