Overview of ISO/ANSI label processing

Label processing is handled by the I/O support routines of data management (open, EOV, and close). Label processing consists of the following basic functions:

Converting input labels from ASCII to EBCDIC and converting output labels from EBCDIC to ASCII
Checking the labels on input tapes to
- Ensure that the correct volume is mounted
- Identify, describe, and protect the data set being processed
- Attempt to ensure maximum correctness and consistency of data sets and their labels
- Identify compatibility conflicts with Version 3 or Version 4 standards
Checking the existing labels on output tapes to
- Ensure that the correct volume is mounted
- Prevent overwriting of vital data
- Identify compatibility conflicts with Version 3 or Version 4 standards
Creating and writing new labels on output tape
For volumes in an automated tape library, comparing the external volume serial number to the magnetically recorded internal label.

These processing functions are summarized in Table 1. The table shows the specific labels that are processed for each function and which routines perform the functions.

Although the default of each IBM-supplied installation exit is to reject the volume, the exits can be modified to do additional label processing. See ISO/ANSI installation exits for more information.

All volumes will be written with Version 3 or Version 4 labels. For information about using tapes with other than Version 3 or Version 4 labels, see Compatibility with non-version 3 or non-version 4 volumes.

Table 1. ISO/ANSI label processing by Open/Close/EOV routines
Processing	Volume Label			Header Labels¹				Trailer Labels¹
Processing	VOL1	VOL 2–9	User Volume Labels	HDR1	HDR2	HDR3-9	UHL	EOF1 or EOV1	EOF2 or EOV2	EOF3-9 or EOV3-9	UTL
First or only volume²
Checks labels on input tape	Open	Ignored³	Ignored³	Open	Open	Ignored³	Open	EOV	Bypassed	Ignored³	EOV
Checks existing labels on output tape before overwriting	Open	Ignored⁴	Ignored⁴	Open	Not read	Not read	Not read	Not read	Not read	Open
Writes new labels on output tape	Open or user⁵	Not written	Not written	Open	Open	Not written	Open	Close or EOV	Close or EOV	Not written	Close or EOV
Compares the volume serial number on the external volume label to the serial number in the tape volume label⁷	Open	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸
Second or subsequent volumes⁶
Checks labels on input tape.	EOV	Ignored³	Ignored³	EOV	Bypassed	Ignored³	EOV	EOV	Bypassed	Ignored³	EOV
Checks existing labels on output tape before overwriting.	EOV	Ignored⁴	Ignored⁴	EOV	Not read	Not read	Not read	Not read	Not read	Not read	Not read
Writes new labels on output tape.	EOV or user⁵	Not written	Not written	EOV	EOV	Not written	EOV	Close or EOV	Close or EOV	Not written	Not written
Compares the volume serial number on the external volume label to the serial number in the tape volume label⁷	EOV	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸	N/A⁸
Notes: For read backward operations, the action on header and trailer labels is reversed. Includes the first volume of concatenated data sets with unlike characteristics when the user program has turned on the DCB unlike attributes bit (DCBOFPPC). See z/OS DFSMS Using Data Sets . Label sequence is checked but contents are ignored. Operator must give Open/EOV permission to overwrite VOL2–9 or ULV labels. User can create the label with the EDGINERS or IEHINITT utility programs, or a user program. Includes the first volume of concatenated data sets when the user has not turned on the DCB unlike attributes bit. Applies only to tape library. Not Available.