remark on large domains

WRF/WRF_basic.md

@@ -306,4 +306,6 @@ Variables are then accessible as `wrf.u`, `wrf.v` etc.
 
 ### Important namelist settings
 
-
+#### Input/output format for large domains
+For domain sizes larger than about 2300x2300x100, it is necessary that `io_form_input` and `io_form_history` are identical.
+Option 11 requires the pnetcdf library to be installed and linked with WRF. With option 102, each process writes its own file. Thus, a joiner program is required that combines all files into one file per timestep.