Cost-Minimization in the Design of IT Infrastructures with Legacy Constraints.

The selection of a cost-minimizing combination of hardware and network components that satisfy requirements is a complex design problem with multiple degrees of freedom. Decisions must be made on how to distribute the computing load onto multiple computers and where to locate computers. Furthermore, legacy components can be differently reused depending on design choices on other infrastructural alternatives and their reuse can affect significantly the total cost of ownership of the system. Legacy systems have often a high residual economic value or they can be upgraded and their life cycle can be extended over a significantly longer period of time with limited additional investments. The reuse of legacy systems becomes a relevant choice which can shift cost-trade-offs. This paper provides an overall methodology for combining hardware and network design in a single cost-minimization problem for multi-site computer systems considering the reuse of legacy systems. Costs are minimized by applying a heuristic optimization approach to a sound decomposition of the problem. Verifications consider several test cases with different computing and communication requirements. Cost reductions are evaluated by comparing the cost of methodological results with those of architectural solutions obtained by applying professional design guidelines.