The SAP mst-instance command is used to create MST instances at the SAP level. MST instance at a SAP level can be created only if MST instances are defined at the service level.
The parameters that can be defined per instance are mst-path-cost and mst-port-priority:
mst-path-cost
Specifies path-cost within a specific MST instance. The path-cost is proportional to link speed.
mst-port-priority
Specifies the port priority within a specific MST instance.