This object identifies which logical unit, matching a specific ciscoScsiLuIndex value, this row maps to a particular LUN number. This is the actual mapping mechanism: an admin creates a row here to say expose logical unit N as LUN X to this initiator or group, so getting this index wrong points a host at the wrong disk entirely. Setting this object to the LU index for a specific data volume, combined with the LUN number implied by the row's own index, is what makes that volume appear as, say, LUN 5 to a particular server.