The OUTSPCE option designates the amount of space for each secondary extent that MFX will obtain for the output data set(s) if it has not been specified in the JCL.
You can give a specific amount of space (nnnn) for each secondary extent. nnnn will be in tracks, cylinders, or blocks, depending on the type of space specified on the DD statement(s).
If this option is not specified, the default is 16.
Specify nnn% (a value followed by a percent sign) to give a percentage of primary space to be used for each secondary extent in the output data set(s).
Specify 0 to signal that no automatic secondary space is to be obtained for the output data set(s).