CERN IT department has been maintaining different HPC facilities over the past five years, one in Windows and the other one on Linux as the bulk of computing facilities at CERN are running under Linux. The Windows cluster has been dedicated to engineering simulations and analysis problems. This cluster is a High Performance Computing (HPC) cluster thanks to powerful hardware and low-latency interconnects. The Linux cluster resources are accessible through HTCondor, and are used for general purpose parallel but single-node type jobs, providing computing power to the CERN experiments and departments for tasks such as physics event reconstruction, data analysis and simulation. For HPC workloads that require multi-node parallel environments for MPI programs, there is a dedicated HPC service with MPI clusters running under the SLURM batch system and dedicated hardware with fast interconnects.
In the past year, it was decided to consolidate compute intensive jobs in Linux to make a better use of the existing resources. Moreover, this was also in line with CERN IT strategy to reduce its dependencies on Microsoft products. This paper describes the migration of Ansys, COMSOL and CST users who were running on Windows HPC to Linux clusters. Ansys, COMSOL and CST are three engineering applications used at CERN on different domains, like multiphysics simulations or electromagnetic field problems. Users of these applications are sitting in different departments, with different needs and levels of expertise. In most cases the users have no prior knowledge of Linux. The paper will present the technical strategy to allow the engineering users to submit their simulations to the appropriate Linux cluster, depending on their HW needs. It will also describe the technical solution to integrate their Windows installations to submit to Linux clusters. Finally, the challenges and lessons learnt during the migration will be also discussed.
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