Top-of-Rack Switching – Better or Worse for Your Data Center? (Part 2)

by Lisa Huff

Last week I gave you some reasons why a Top-of-Rack (ToR) switching architecture could be higher cost for your data center network. Today, I’d like to discuss the advantages of using a ToR switching topology.

1) CLOS network architecture – in order to support this, you most likely need to use a ToR switch. For those not familiar with the CLOS network, it is a multi-stage network whose main advantage is that it requires fewer cross-points to produce a non-blocking structure. It is difficult and can be more costly to implement a non-blocking network without CLOS.

2) Latency and throughput – while it may be counter-intuitive, there may be less latency in your network if you use a ToR switch architecture. The main reason really has little to do with the switch itself and more to do with the data rate of your network. 10-Gigabit Ethernet typically has about 1/5th the latency that Gigabit Ethernet does. It also obviously has the capability of 10 times the throughput – provided that your switches can support line-rate (their backplanes can handle 10 Gbps). So implementing 10GigE in your equipment access layer of your data center can seriously reduce the amount of time data takes to get from initiator to destination. This, of course, is more critical in some vertical markets than in others – like the financial sector where micro-seconds can make a difference of millions of dollars made or lost.

A comment on latency and throughput however – if this is so critical, why not use InfiniBand instead of Ethernet ToR switches? It seems to me that InfiniBand already has these issues solved without adding another switch layer to the network.