<!-- You can erase any parts of this template not applicable to your issue. --> ### Description Large meshes created for instance with AddLayer tool can not be saved into a vtu: The error message is: ``` ERROR: In /build/vtk/src/VTK-8.2.0/IO/XML/vtkXMLWriter.cxx, line 1372 vtkXMLUnstructuredGridWriter (0x55f242c1b0d0): Array "connectivity" is too large. Set HeaderType to UInt64. ``` ## Steps to Reproduce the Problem 1. Use a large mesh (the current mesh has 84x10^6 elements) and add an additional layer (this should add another 14x10^6 elements) **Expected behavior:** Write the mesh to file. **Actual behavior:** AddLayer (and probably other tools creating large meshes) crashes. ## Specifications - Version: AddLayer version: 6.3.0-984-gc7f0e7b38 - Platform: envinf1 / arch linux