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Parallel I/O with NetCDF-4

NetCDF-4 provides access to HDF5 parallel I/O features for netCDF-4/HDF5 files.

NetCDF classic and 64-bit offset format may not be opened or created for use with HDF5-based parallel I/O. (They may be opened and created, but parallel I/O is not available.) They may be opened or created for use with parallel-netcdf-based parallel I/O. A few functions have been added to the netCDF C API to handle parallel I/O. You must build netCDF-4 properly to take advantage of parallel features (see Building with Parallel I/O Support ).

The nc_open_par() and nc_create_par() functions are used to create/open a netCDF file with parallel access.

Note
The parallel access associated with these functions is not a characteristic of the data file, but the way it was opened.

Collective/Independent Access

Parallel file access is either collective (all processors must participate) or independent (any processor may access the data without waiting for others). All netCDF metadata writing operations are collective. That is, all creation of groups, types, variables, dimensions, or attributes. Data reads and writes (ex. calls to nc_put_vara_int() and nc_get_vara_int()) may be independent (the default) or collective. To make writes to a variable collective, call nc_var_par_access().


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