Simulink will create DMR files in the temporary directory to store data for logged signals. This can include data from signals marked for logging, data logged from output ports, data sent to To Workspace blocks, or many of the other signal logging methods specified in this table.
By default, simulation data logs to disk with data loaded into memory on demand, and the maximum size of logged data is constrained only by available disk space. You can use the Simulation Data Inspector settings to specify global limits on the amount of data saved as well as change the location where data is saved. For more info, review the page: Configure the Simulation Data Inspector (For 2020a please see this bug report)
You can also reduce the size of the generated DMR files by reducing the amount of logged data. Review your data logging settings in the Model Configuration Parameter: Data Import/Export pane for areas where data is logged which is not needed. To reduce the number of logged signals temporarily for a set of runs, consider using the Data Logging Override options. Note that data logging overrides can be changed and applied on a model in accelerator mode without requiring rebuilding the model.
As a final note, these files should be automatically deleted upon MATLAB close. However the auto-cleanup may be missed if MATLAB terminated improperly, such as if the process is killed by the user through the OS or if MATLAB crashes. In which case it is safe to delete these files from your temporary directory.
