The segment delete byte

The bits in the delete byte are only meaningful for logical child segments and their logical parents. For segments involved in a logical relationship, the PD and LD bits are set or assumed set as follows:

• If a segment is physically deleted (thereby preventing further access to it from its physical parent), then delete processing scans downward from the deleted segment through its dependents, turns upward, and either releases each segment's DASD space or sets the PD bit. HISAM is the one exception to this process. In HISAM, the delete bit is set in the segment specified by the DLET call and processing terminates.
• If the PD bit is set in a logical parent, the LD bit is set in all logical children that can be reached from that logical parent.
• When physical pairing is used, if the PD bit is set in one of a pair of logical children, the LD bit is set in its paired segment.
• When a virtually paired logical child is logically deleted (thereby preventing further access to it from its logical parent), the LD bit is set in the logical child.
• The LD bit is assumed set in all logical children in unidirectional logical relationships.
• If physical pairing is used, the LD bit is assumed set in a parent if all the paired segments that are physical children of the parent have the PD bit set on.