Appia and the HP SAN Designer: automatic storage area network fabric design

Designing a SAN fabric involves finding a network of hubs, switches and links to connect hosts to their storage devices. The network must be capable of simultaneously meeting the data flow requirements between multiple host-device pairs, and it must do so cost-effectively, since large-scale SAN fabrics can cost millions of dollars. Moreover, the network must be robust to failures of fabric elements. Given that the data flows can number in the hundreds, simple over-provisioned manual designs are often not attractive; they cost significantly more than they need to, may not meet the performance needs, may expend valuable resources in the wrong places, and are subject to human error. Producing SAN fabric designs automatically can address these difficulties, but it is a non-trivial problem; it extends the NPhard minimum-cost fixed-charge multicommodity network flow problem to include degree constraints, node capacities, node costs, unsplittable flows, and other requirements. Nonetheless, we have developed two efficient algorithms for automated SAN fabric design. We give an overview of these algorithms and compare their performance over a range of design problems. We also discuss how they have been extended to reprovision existing SAN fabrics. Finally, we describe how, through the creation of the HP SAN Designer tool, these algorithms have been transferred to the HP SAN design community with the expert help of the Network and Storage Support Services Organization.