The Portal Group Tag (PGT) for the registered iSCSI Portal
Group object in an iSNS Server instance. This indicates
the tag value that the Portal uses for access to the iSCSI
Storage Node. The PGT is used for coordinated access between
multiple Portals, as described in the iSCSI Specification
[iSCSI]. The value of zero indicates a NULL value, or no
association.