Exploring server redundancy in nonblocking multicast data center networks

Clos networks and their variations such as folded- Clos networks (fat-trees) have been widely adopted as network topologies in data center networks. Since multicast is an essential communication pattern in many cloud services, nonblocking multicast communication can ensure the high performance of such services. However, nonblocking multicast Clos networks are costly due to the large number of middle stage switches required. On the other hand, server redundancy is ubiquitous in today's data centers to provide high availability of services. In this paper, we explore server redundancy in data centers to reduce the cost of nonblocking multicast Clos data center networks (DCNs). First, we show that the sufficient nonblocking condition on the number of middle stage switches for multicast Clos DCNs can be significantly reduced, when the data center is 2-redundant, i.e., each server in the data center has exactly one redundant backup. We then investigate more general cases that the data center is k-redundant (k > 2), and show that a higher redundancy level further reduces the cost of nonblocking multicast Clos DCNs. We also extend the result to practical data centers where servers may have different number of redundant backups depending on the availability requirement of services provided. Finally, we provide a multicast routing algorithm with linear time complexity to configure multicast connections in Clos DCNs.