A target portal group tag is a numerical value from 0 to 65535 that identifies a specific iSCSI target portal group. Once a tag is assigned to a target portal group, you cannot change the tag.
When modifying target portal groups for clustered filers, make sure the interfaces on each filer fail over to an interface assigned to a target portal group with the same tag on the partner filer. If the target portal group tags do not match at the time of the takeover operation, the initiator will see a different mapping between the target portal and its target portal group. The mismatch can prevent the initiator from reestablishing the multi-connection session to the takeover filer.