The INITIALSIZE keyword specifies the number of blocks in the initial storage allocation (extent) for a disk file. This information is used by the EXTENDSIZE keyword, which specifies the number of blocks by which a disk file is extended each time more space is needed for a file. The INITIALSIZE keyword takes the following form:
INITIALSIZE = insz
If you do not specify INITIALSIZE or you specify zero, no initial allocation is made. The system attempts to allocate contiguous space for INITIALSIZE. If not enough contiguous space is available, noncontiguous space is allocated.
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.