Unless you explicitly code the SPACE parameter for the new data set, the system
determines the space to be allocated for the new data set by adding up the space
allocated in the first three extents of the model data set. Therefore, the space
allocated for the new data set will generally not match the space that was
specified for the model data set. Note that regardless of the units in which the
model data set was allocated, the new data set will be allocated in tracks. This
assumes that space was not specified on the JCL and is being picked up from
the model data set.