Version 3 or Version 4 Volumes: If the volume is RACF protected, and the volume security processing has not been suppressed, the RACHECK installation exits are entered to accept or reject the volume (by a return code from RACHECK). If the VOL1 accessibility field contains a valid Version 3 or Version 4 character, the RACHECK parameter list is initialized to address the ISO/ANSI exit parameter list (IECIEPRM) and the accessibility code. Otherwise, the RACHECK installation exits are passed zeroed pointers for the ISO/ANSI parameters. If RACF accepts the volume but the ISO/ANSI parameters to the exit are zero, the validation suppression exit is entered.

If RACF is not available, or the volume is not defined to RACF, OPEN/EOV checks the accessibility field in the VOL1 label. If the field contains a valid Version 3 or Version 4 character, the volume access exit is entered to accept or reject the volume (by a return code in the exit parameter list). If the field contains a space, the validation suppression exit is entered. All other characters cause the volume to be rejected.

The VOL1 accessibility code can be changed when the VOL1 label is changed by the EDGINERS or IEHINITT utility programs or by the operator during open. See Volume label.

Version 1 Volumes: First, OPEN/EOV checks the accessibility field in the VOL1 label. If the field contains a space character, the volume is defined to RACF, and volume security processing has not been suppressed, then the RACHECK installation exits are entered to accept or reject the volume (by a return code from RACHECK). Access to the volume is allowed if the field contains a space character, but the volume is not defined to RACF, or the volume security processing has been suppressed. Each data set on the volume can be individually protected. The volume is rejected if the field contains anything other than a space character.

The VOL1 accessibility code can be changed when the VOL1 label is changed by the EDGINERS or IEHINITT utility programs, or by the operator during open. See Volume label.