Exponential growth in data center usage has been responsible for driving a huge amount of investment in the networking infrastructure used to connect virtualized servers to the multiple services they now need to accommodate. To support the server-to-server traffic that virtualized data centers require, the networking spine will generally rely on high capacity 40 Gbit/s and 100 Gbit/s switch fabrics with aggregate throughputs now hitting 12.8 Tbit/s. But the ‘one size fits all’ approach being employed to develop these switch fabrics quickly leads to a costly misalignment for data center owners. They need to find ways to match the interfaces on individual storage units and server blades that have already been installed with the switches they are buying to support their scale-out plans.
The top-of-rack (ToR) switch provides one way to match the demands of the server equipment and the network infrastructure. The switch can aggregate the data from lower speed network interfaces and so act as a front-end to the core network fabric. But such switches tend to be far more complex than is actually needed - often derived from older generations of core switch fabric. They perform a level of switching that is unnecessary and, as a result, are not cost effective when they are primarily aggregating traffic on its way to the core network’s 12.8 Tbits/s switching engines. The heightened expense manifests itself not only in terms of hardware complexity and the issues of managing an extra network tier, but also in relation to power and air-conditioning. It is not unusual to find five or more fans inside each unit being used to cool the silicon switch. There is another way to support the requirements of data center operators which consumes far less power and money, while also offering greater modularity and flexibility too.
Providing a means by which to overcome the high power and cost associated with traditional ToR switch designs, the IEEE 802.1BR standard for port extenders makes it possible to implement a bridge between a core network interface and a number of port extenders that break out connections to individual edge devices. An attractive feature of this standard is the ability to allow port extenders to be cascaded, for even greater levels of modularity. As a result, many lower speed ports, of 1 Gbit/s and 10 Gbits/s, can be served by one core network port (supporting 40 Gbits/s or 100 Gbits/s operation) through a single controlling bridge device.
With a simpler, more modular approach, the passive intelligent port extender (PIPE) architecture that has been developed by Marvell leads to next generation rack units which no longer call for the inclusion of any fans for thermal management purposes. Reference designs have already been built that use a simple 65W open-frame power supply to feed all the devices required even in a high-capacity, 48-ports of 10 Gbits/s. Furthermore, the equipment dispenses with the need for external management. The management requirements can move to the core 12.8 Tbit/s switch fabric, providing further savings in terms of operational expenditure. It is a demonstration of exactly how a more modular approach can greatly improve the efficiency of today's and tomorrow's data center implementations.