OpenLB – Open Source Lattice Boltzmann Code › Forums › on OpenLB › General Topics › Storing data in a csv file error (running code in parallel) › Reply To: Storing data in a csv file error (running code in parallel) July 12, 2021 at 2:33 pm #5815 AdrianKeymaster You have to ensure that the IO only happens in the main process (where BlockDataSyncMode::ReduceOnly syncs to). Otherwise each process will write to the same file in parallel and in addition not even have the correct data.