Modernizing Legacy Codes for Next-Generation Storage Infrastructures: A Case Study of PALM on Intel DAOS

<!--HTML-->We present our early experiences with the Distributed Asynchronous Object Storage (DAOS) focusing on its usage for checkpointing with the real-world scientific application PALM. The presentation includes an introduction of the of large eddy simulation and its legacy Fortran IO checkpointing mechanism. A thin software layer is introduced to remove the hard-coded IO operations by generic API calls. This abstraction enables the application to support both Fortran Stream IO, MPI IO, as well as netCDF on top of HDF5 which is the principal foundation for using DAOS in our use-case. We present early performance numbers on a Cascade Lake test system with Optane DCPMM and a comparison with the Lustre-based infrastructure of the HLRN-IV phase 1 system. The talk also presents some of the lessons learned from adjusting the application's legacy checkpointing code to a modern software environment.