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Writing to a Dataset by Chunk

In this example each process writes a "chunk" of data to a dataset. The C and Fortran 90 examples result in the same data layout in the file.

Figure a C Example Figure b FORTRAN 90 Example

For this example, four processes are used, and a 4 x 2 chunk is written to the dataset by each process.

To do this, you would:

Use the block parameter to specify a chunk of size 4 x 2 (or 2 x 4 for Fortran 90).

Use a different offset (start) for each process, based on the chunk size:

C:
 Process 0        Process 1       Process 2       Process 3
 ---------        ---------       ---------       ---------
 offset[0] = 0    offset[0] = 0   offset[0] = 4   offset[0] = 4 
 offset[1] = 0    offset[1] = 2   offset[1] = 0   offset[1] = 2 

FORTRAN 90:
 offset(1) = 0    offset(1) = 2   offset(1) = 0   offset(1) = 2
 offset(2) = 0    offset(2) = 0   offset(2) = 4   offset(2) = 4

For Process 2 the offset and block parameters would look like:

Figure a C Example Figure b FORTRAN 90 Example

Below is an example program for writing hyperslabs by chunk in Parallel HDF5:

C Example

Hyperslab_by_chunk.c

F90 Example

hyperslab_by_chunk.f90

The following is the output from h5dump for the HDF5 file created with this example:

HDF5 "SDS_chnk.h5" {
GROUP "/" {
   DATASET "IntArray" {
      DATATYPE  H5T_STD_I32BE  
      DATASPACE  SIMPLE { ( 8, 4 ) / ( 8, 4 ) } 
      DATA {
         1, 1, 2, 2,
         1, 1, 2, 2,
         1, 1, 2, 2,
         1, 1, 2, 2,
         3, 3, 4, 4,
         3, 3, 4, 4,
         3, 3, 4, 4,
         3, 3, 4, 4
      } 
   } 
} 
}

The h5dump utility is a C program, and the output is in C order.

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The HDF Group
Last Modified: February 20, 2007

Figure a `C Example`	Figure b `FORTRAN 90 Example`