The EXTENDSIZE specifier indicates the number of blocks by which to extend a disk file (extent) when additional storage space is needed. It takes the following form:
EXTENDSIZE = es
If you do not specify EXTENDSIZE or if you specify zero, the process or system default for the device is used.
For details on the relationship between the EXTENDSIZE specifier and the INITIALSIZE specifier, see Section 12.6.15.