HDF5 output fails at large meshes .

[Jalil Khan]

Dear all,

I am encountering an issue with HDF5/XDMF output using DataOut::write_hdf5_parallel() on large meshes. Up to a resolution of 256×256×256, everything works correctly, but at 512×512×512 the program aborts with the following HDF5 error:

```
#014 HDF5-DIAG: Error ... unable to set chunk sizes
    major: Dataset
    minor: Bad value
#015 HDF5-DIAG: ... chunk size must be < 4GB
```

I have attached the error log as well.

From inspecting the source in data_out_base.cc, HDF5 uses chunked layout, with chunk dimensions set internally in deal.II. At 512³, the computed chunk size exceeds the HDF5 hard limit of 4 GB per chunk, which leads to the failure.

Is there a recommended way for users to avoid this error when writing large output files?

I would really appreciate any suggestions.

Thank you.

Best Regards,

JRK