Hedera: dynamic flow scheduling for data center networks

Today’s data centers offer tremendous aggregate band-width to clusters of tens of thousands of machines. However, because of limited port densities in even the highest-end switches, data center topologies typically consist of multi-rooted trees with many equal-cost paths between any given pair of hosts. Existing IP multi-pathing protocols usually rely on per-flow static hashing and can cause substantial bandwidth losses due to long-term collisions. In this paper, we present Hedera, a scalable, dy-namic flow scheduling system that adaptively schedules a multi-stage switching fabric to efficiently utilize aggre-gate network resources. We describe our implementation using commodity switches and unmodified hosts, and show that for a simulated 8,192 host data center, Hedera delivers bisection bandwidth that is 96 % of optimal and up to 113 % better than static load-balancing methods.