  In the traditional two-rack distributed storage system (DSS) model, due to
the assumption that the storage capacity of each node is the same, the minimum
bandwidth regenerating (MBR) point becomes infeasible. In this paper, we design
a new non-homogeneous two-rack model by proposing a generalization of the
threshold function used to compute the tradeoff curve. We prove that by having
the nodes in the rack with higher regenerating bandwidth stores more
information, all the points on the tradeoff curve, including the MBR point,
become feasible. Finally, we show how the non-homogeneous two-rack model
outperforms the traditional model in the tradeoff curve between the storage per
node and the repair bandwidth.
