For downstream LUs, the PeerPuIndex identifies
the upstream PU that owns the upstream LU to
which this downstream LU is assigned.
For upstream LUs, the PeerPuIndex identifies
the downstream PU that owns the downstream LU
to which this upstream LU is assigned.
If PeerPuIndex is zero, the LU is a pooled LU and has
not been assigned a peer LU from the pool.