Opening an output data set

If IBM standard labels are specified, the first existing record on the output tape must be an IBM standard volume label (VOL1). At the time the data set is opened, the system checks the first existing record on the tape to determine whether the record is 80 bytes long and contains the identifier VOL1 in the first 4 bytes. The various error conditions that can occur during verification of the first record are explained in IBM standard volume label editor routines.

If the system-wide RACF tape protection option has been specified and the DD statement has specified PROTECT=YES, and the DD statement has not been previously opened for output processing, open ensures the PROTECT=YES specification is valid. Both the volume sequence number and the file sequence number must be set to 1, and a private volume must be requested. The protection indicator in the JFCB is reset so that subsequent OPENs of that DD statement for output processing do not attempt validity checking (of the PROTECT=YES specification) and defining the volume to RACF.

Attention: Doing multiple opens and closes without writing any user data in the end-of-tape reflective marker area can result in the writing of header and trailer labels past the reflective marker. Access methods detect the reflective markers; however, since the creation of empty data sets does not involve access methods, the end-of-tape marker is not detected. This can cause the reel or cartridge to run out of tape.