When a data set is opened for output, processing is similar to opening for input, except that:

• Only Version 3 or Version 4 tapes are created for output processing.
• If the system-wide RACF tape protection option has been specified, and the DD statement has specified PROTECT=YES but has not previously been opened for output processing, OPEN ensures that 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 definition of the volume to RACF.
• The label anomaly exit and volume label editor are entered for label conflicts or for version conflicts (the label is not Version 3 or Version 4) if output is to the first data set. If output is to any data set other than the first data set, or if the first data set is allowed to be extended, a version compatibility conflict causes the volume to be rejected.
• An action message is issued to the operator if the tape is file protected (to allow writing).
• If the system-wide RACF tape protection option has been specified, RACF authorization at the UPDATE level is checked. If a Version 3 or Version 4 tape is not RACF protected, the volume accessibility code is checked as it is for input processing. For additional information, see Protecting data.
• Symmetry violations during output to a Version 3 volume occur if the open option is EXTEND or OUTINX. Open for OUTPUT or OUTIN with DISP=MOD during output also violates symmetry. Open for OUTPUT or OUTIN with DISP=MOD is checked after the volume has been positioned. An EXCP DCB is checked to ensure the presence of a device-dependent area large enough to contain a block count.

If a density conflict occurs, the label anomaly installation exit and possibly the volume label editor are entered. If the conflict occurs for the first data set on the volume, a new volume label (Version 3 or Version 4) is written in the density specified by the user. For other than the first data set, the data set header labels are written in the density of the volume label at the beginning of the tape, unless the volume label editor is modified. If the old volume label is longer than 80 characters, the excess characters are lost unless:

• The IBM-supplied volume label editor is replaced with a program that protects the extra data during a density conflict before returning to open/EOV for reverification of the volume, or
• The operator rejects a rewrite of the label by a response to message IEC704A L or IEC704A L UVL.

For compaction capable tape drives, the system enforces single mode recording. This results in the second and subsequent data sets on the volume being written in the same mode as the first data set. Since the existing mode is determined by information in the volume label, single mode recording is not enforced for NL volumes.