Data Centres Need Green Switches

Talk about green data centres usually focuses on servers and how to cool them. But network switches usually get more or less ignored.

There are good reasons for this, as the network probably amounts to a few percent of the energy needs of a data centre. But that proportion is increasing, and data centres need greener switches, as well as switches that can handle specific needs – or at least that’s the view of Stephen Garrison of data centre Ethernet provider Force10.

Keeping energy use down

Energy use of the network equipment in data centres has had comparatively little exposure, simply because it is small compared to the use by servers, admitted Garrison, but other vendors, notably Brocade, have made energy comparisons with Cisco.

Force10 has always aimed for energy efficiency, Garrison said, and a comparison by test house Tolly has just found that its switches use around half the power of those of Cisco or Juniper.

The issue has become important, because in virtualised data centres, data traffic increases for a given number of servers, and the proportion of power used by network switches goes up. “The cloud leads to bursty traffic,” said Garrison, “like rogue waves in the sea.”

Because there are fixed limits to the power available in most data centres, for many people lower power has become a key goal. Some people’s business bonus depends on achieving a lower PUE (Power Usage Effectiveness), he said.

The power difference is not due to changes in the Ethernet standard (though there is an Energy Efficient Ethernet aimed at the campus), said Garrison. It’s all down to efficiencies in the design, and to taking care of details such as the efficiency of the power supply unit.

The data centre is different

Garrison is in London for the 360IT event, and wants to reassert the role of a specialist in data centre Ethernet, alongside other vendors like Juniper and Cisco, whose focus is more on service providers.

“A fast, non-blocking switch is not enough in a data centre,” Garrison contended. Those rogue waves of traffic will wash around faster and faster, as data centre users get used to spinning up virtual machines that are parked on disks, whenever they need them.

So a data centre switch is a different beast, he said. It has to have intelligence, and good buffers. The vendor also has to perform a balancing act – making the switch aware of different technology providers, but not tying itself exclusively to any.