H5P_SET_FAPL_MULTI sets the file access property list fapl_id to use the multi-file driver.

The multi-file driver enables different types of HDF5 data and metadata to be written to separate files. These files are viewed by the HDF5 library and the application as a single virtual HDF5 file with a single HDF5 file address space. The types of data that can be broken out into separate files include raw data, the superblock, B-tree data, global heap data, local heap data, and object headers. At the programmer's discretion, two or more types of data can be written to the same file while other types of data are written to separate files.

The array memb_map maps memory usage types to other memory usage types and is the mechanism that allows the caller to specify how many files are created. The array contains H5FD_MEM_NTYPES entries, which are either the value H5FD_MEM_DEFAULT or a memory usage type. The number of unique values determines the number of files that are opened.

The array memb_fapl contains a property list for each memory usage type that will be associated with a file.

The array memb_name should be a name generator (a printf-style format with a %s which will be replaced with the name passed to H5FDopen, usually from H5F_CREATE or H5F_OPEN).

The array memb_addr specifies the offsets within the virtual address space, from 0 (zero) to HADDR_MAX, at which each type of data storage begins.

If relax is set to TRUE (or 1), then opening an existing file for read-only access will not fail if some file members are missing. This allows a file to be accessed in a limited sense if just the meta data is available.

Default values for each of the optional arguments are as follows:

H5FD_MEM_SUPER -> 0 * (HADDR_MAX/6)
H5FD_MEM_BTREE -> 1 * (HADDR_MAX/6)
H5FD_MEM_DRAW -> 2 * (HADDR_MAX/6)
H5FD_MEM_GHEAP -> 3 * (HADDR_MAX/6)
H5FD_MEM_LHEAP -> 4 * (HADDR_MAX/6)
H5FD_MEM_OHDR -> 5 * (HADDR_MAX/6)
            

Returns a non-negative value if successful. Otherwise returns a negative value.

The following code sample sets up a multi-file access property list that partitions data into meta and raw files, each being one-half of the address:

                  H5FD_mem_t mt, memb_map[H5FD_MEM_NTYPES];
                  hid_t memb_fapl[H5FD_MEM_NTYPES];
                  const char *memb[H5FD_MEM_NTYPES];
                  haddr_t memb_addr[H5FD_MEM_NTYPES];
 
                  // The mapping...
                  for (mt=0; mt<H5FD_MEM_NTYPES; mt++) {
                     memb_map[mt] = H5FD_MEM_SUPER;
                  }
                  memb_map[H5FD_MEM_DRAW] = H5FD_MEM_DRAW;
 
                  // Member information
                  memb_fapl[H5FD_MEM_SUPER] = H5P_DEFAULT;
                  memb_name[H5FD_MEM_SUPER] = "%s.meta";
                  memb_addr[H5FD_MEM_SUPER] = 0;
 
                  memb_fapl[H5FD_MEM_DRAW] = H5P_DEFAULT;
                  memb_name[H5FD_MEM_DRAW] = "%s.raw";
                  memb_addr[H5FD_MEM_DRAW] = HADDR_MAX/2;
 
                  hid_t fapl = H5Pcreate(H5P_FILE_ACCESS);
                  H5Pset_fapl_multi(fapl, memb_map, memb_fapl,
                                  memb_name, memb_addr, TRUE);