Data set accessibility

If a volume is RACF protected, and access to the volume was checked when the volume was verified (by RACHECK processing), then data set accessibility fields are not checked; therefore, any data set on the volume can be accessed. If a volume is not RACF protected, then the system inspects the accessibility field in the HDR1 label of the requested data set. For a multivolume data set, the system inspects the HDR1 label on each volume. The accessibility codes of any concatenated data sets are also inspected.

Version 3 or Version 4 Volumes: 1 or 3 in the data set accessibility field with a system code of "IBMZLA" indicates an MVS password-protected data set; a space character in the accessibility field allows unlimited access; and a valid Version 3 or Version 4 character causes the file access exit to be entered for authorization processing. The file access exit is also entered when a new data set is added to an output volume and if the first character of the JCL ACCODE keyword is a valid character. Any other character causes the volume to be rejected.

If the accessibility field of a data set being opened contains a valid character or a space, no attempt is made to check the accessibility field of any other data sets that may exist on the volume; therefore, the other data sets can be overlaid by new output. If accessibility checking for multiple data sets is required, it must be done by an installation-written file access exit. Never place an access-protected data set on the same volume with unprotected data sets because no exit is entered for unprotected data sets.

An HDR1 accessibility code of valid character can be specified by the ACCODE parameter of JCL. ACCODE can also be specified for dynamic allocation (SVC 99 key). Changes to an HDR1 accessibility code of a valid character can be monitored by an installation-written file access exit. Password codes override ACCODE values if both are simultaneously specified.

Version 1 Volumes: 1 or 3 in the data set accessibility field indicates a password-protected data set.

A space character in the accessibility field allows unlimited access, and no attempt is made to check the accessibility field of any other data sets that may exist on the volume; therefore, the other data sets may be overlaid by new output.