A table containing currently registered and unregistered
portal objects that have been explicitly assigned to specific
DDs. Explicit assignment of a portal to a DD is only done
when a specific set of portals are preferred for use within a
DD. Otherwise, for iSCSI, the Portal Group Object should be
used for identifying which portals provide access to which
storage nodes. The number of rows in the table is dependent
on the number of explicit relationships between portals and
DDs registered in the iSNS.