Weather and climate models are being more complex in order to solve new features as eddies and clouds properly. For example, increasing the spatial resolution of their simulations or adding new additional coupled components. As a consequence, more computational resources are needed to maintain a suitable execution time. Moreover, these new coupled and high-resolution simulations will produce massive outputs where post-processing output will a considerable time. This means that the management of Input/Output (I/O) and post-processing will increase in cost, complexity and size and additional approaches are needed to make our models more scalable. Moreover, additional cost is needed to convert output data of IFS/OpenIFS to standard formats as NetCDF, a requirement for example for CMIP project. These are some of the reasons why the XML I/O Server (XIOS), an asynchronous MPI parallel I/O server that is able to post-process data online and write it in NetCDF format, is being integrated to OpenIFS.

In this work, we present computational aspects and the performance evaluation done for this integration, showing how to do an efficient integration and which particular aspects have to be take into account to increase the computational performance. Different issues related to XIOS and the integration process will be explained. From issues which could reduce the performance of a XIOS integration to general aspects of atmospherical models needed for the integration. Different techniques implemented will be also explained, such as shared memory techniques using OpenMP for data movement or asynchronal communications to overlap OpenIFS calculations with XIOS work. Profiling analysis will be also shown to explain all the details.