The INITIALSIZE specifier indicates the number of blocks in the initial storage allocation (extent) for a disk file. This information is used by the EXTENDSIZE specifier, which indicates the number of blocks by which a disk file is extended each time more space is needed for a file. The INITIALSIZE specifier takes the following form:
If you do not specify INITIALSIZE or if you specify zero, no initial allocation is made. The system attempts to allocate contiguous space for INITIALSIZE, but noncontiguous space is allocated if there is not enough contiguous space available.
INITIALSIZE is effective only at the time the file is created. If EXTENDSIZE is specified when the file is created, the value specified is the default value used to allocate additional storage for the file.
If you specify EXTENDSIZE when you open an existing file, the value you specify supersedes any EXTENDSIZE value specified when the file was created, and remains in effect until you close the file. Unless specifically overridden, the default EXTENDSIZE value is in effect on subsequent openings of the file.