• If you use DSN=NULLFILE on your DD statement for an input data set, a system restriction prevents DFSORT from using the EXCP access method.
• Empty input data sets can be used.
• If any of the input data sets are on tape without standard labels, DCB parameters must be specified on their DD statements.
• ISO/ANSI Version 1 tape files can only be used as input—never as output.
• DFSORT sets appropriate BUFNO values for the input and output data sets; specifying BUFNO in the DD statements for these data sets has no effect.

See SORTIN DD statement for additional considerations.