If you specify that an input or output tape has a Version 3 or Version 4 label, the operating system checks for the Version 3 or Version 4 volume label at the beginning of the tape.

Because of conflicting label types or conflicting tape characteristics, various error conditions can occur during the verification of the first record. Under some error conditions, the tape is accepted for use. Under other error conditions, the tape is not accepted, and the system issues another mount message. For certain other error conditions, the system gives control to a label anomaly exit routine and to a volume label editor routine; your installation can use IBM-supplied routines or it can supply its own routines.

The IBM-supplied volume label editor routines determine the discrepancies between the requested tape and the mounted tape and, if necessary, pass control to the appropriate system routine to create or destroy labels. If DFSMSrmm is controlling the volume, the DFSMSrmm label editor routine controls the creation or destruction or standard labels using RACF profiles in the FACILITIES class. Installation-supplied routines can perform other functions.

IBM recommends using tape management exit routines instead of the volume label editor routines.

For detailed information about these and other available exit routines, see z/OS DFSMS Installation Exits.