Updates on usage of the Czech national HPC center

The distributed computing of the ATLAS experiment at LHC has used computing resources of the Czech national HPC center IT4Innovations for several years. The submission system is based on ARC-CEs installed at the Czech Tier2 site (praguelcg2). Recent improvements of this system will be discussed here. First, there was a migration of the ARC-CE from version 5 to 6 which improves the reliability and scalability. A shared filesystem built on top of sshfs 3.7 no longer represents performance bottleneck. It provided an order of magnitude better transfer performance. New Singularity containers with full software stack can easily fit default resource limits on the IT4I cluster filesystem. A new submission system, allowing sequential running of payloads in one job, was set and adapted to HPC's environment, improving usage on worker nodes with very high number of cores. Overall, the whole infrastructure provides significant contribution to resources provided by praguelcg2.