If you use NOFASTSRT or an input procedure, DFSORT does not know the size of the file that you are sorting. This can lead to an out-of-space condition when you sort large files or to overallocation of resources when you sort small files.
If this occurs, you can use the SORT-FILE-SIZE special register to help DFSORT determine the amount of resource (for example, workspace or hiperspace) needed for the sort. Set SORT-FILE-SIZE to a reasonable estimate of the number of input records. This value is passed to DFSORT as its FILSZ=En value.