Data set Trailer labels

The data set trailer label 1 (EOV1, EOF1) is required for ISO/ANSI labeled tapes. The standard EOV1 and EOF1 labels duplicate the standard HDR1 label so that the tape can be read backward. The EOV1 and EOF1 labels are identical to a HDR1 label except that:

The identifier is EOV or EOF instead of HDR.
A block count is recorded in the first EOV1 or EOF1 label and is used on input to verify that all blocks of the data set are processed. The block count field in the HDR1 label contains zeros (which is what the EOF1/EOV1 block count is reduced to when the data set is read backward).

A data set can be extended by a job different from the one that started writing it. You might do that with DISP=MOD on the DD statement or with the OPEN macro options EXTEND, OUTINX or INOUT. On a Version 3 tape these are allowed only if the installation's label validation exit allows it. Extending a data set might result in fields such as these differing between headers and trailer labels: job name, step name, creation date, expiration date.

Eighty-character Version 3 or Version 4 EOV1 and EOF1 labels are created by the system when the data set is recorded on tape. EOV1 and EOF1 labels created by non-MVS systems must be up to 80 characters long; any characters after position 80 are not used for checking or verification.

Although they are optional, the EOV2 and EOF2 labels are produced by the operating system. These labels are treated similarly to IBM EOV2 and EOF2 labels. If the EOV2 or EOF2 labels are produced by another system, then the "reserved for operating system" fields are not processed.

Labels identified as EOV3-EOV9 or EOF3-EOF9 are allowed but checked for valid label identification and correct sequencing if they are among the trailer labels of a requested data set. The system does not create optional trailer labels beyond the second label.