Label validation

Labels and program specifications for labels and file structure are checked to ensure that a tape format does not violate Version 3 or Version 4 standards. The label validation exit is entered if any of the following requirements are not met:

Labels must contain only certain ASCII characters. For a list of the characters, see Label definition and organization.
Label fields must contain properly aligned data. For more information, see Label definition and organization.
Labels that frame a data set must be symmetrical:
- DISP=MOD is not allowed for extending an existing Version 3 data set or an existing non-IBM format Version 4 data set; however, it can be specified to create a new data set.
- An open option for EXTEND, OUTINX, or INOUT is not allowed in Version 3 or non-IBM format Version 4.
- An EXCP DCB used for output must contain at least a 4-word device dependent area.
For more information, see Data set Trailer labels, Creating a volume label, and z/OS DFSMS Installation Exits.
Block size must not exceed 2␠048 bytes for Version 3 or 32␠760 bytes for Version 4. See Format of ISO/ANSI data set label 2 (HDR2/EOV2/EOF2).
Variable length records must be specified as Format-D, not as Format-V. Undefined-length records (Format-U) are allowed only for Version 1 input volumes; they are not allowed for Version 3 or Version 4 volumes.
Duplicate data set names, including names for generation data sets, are not allowed on the same Version 3 volume. See Processing the HDR1 label.
Expiration dates for successive data sets on a Version 3 volume must not be in ascending sequence. See Expiration date on existing label.