Green Photonics for Energy Efficient Data Centers

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Arlon Martin is the VP of Marketing, Contracts & Government Affairs for Kotura. Martin has more than 25 years of experience in sales, marketing, product and technical management in the semiconductor and optoelectronics industries.

Arlon MartinARLON MARTIN
Kotura

Large data centers are measured by three metrics: number of server blades; number of square feet and megawatts of power.  Rich Miller provided a very nice special report on large data centers in Data Center Knowledge in April 2010. The largest data center in the world, the Lakeside Technology Center, 350 East Cermak, Chicago, covers over 1 million square feet and is supported by 100 MW of power.  Even the smaller data centers of the Top Ten are larger than half a dozen football fields.

The number of server blades is not often disclosed, but we do know that the Microsoft Chicago Data Center has capacity for 224,000 server blades in 110 containers on the ground floor plus room for thousands more in racks in the upstairs area. Worldwide, IDC estimates that over 7 million server blades are sold each year so it is not unusual for a large data center to have 100,000 servers or more.

Data Centers Use Growing Amounts of Energy

Altogether, data centers are estimated to consume a phenomenal 3 percent of the entire power in the U.S. They consume 100 billion kWh at an estimated cost of $7.4B/year. Because they consume so much energy, data center architects are looking at every way possible to reduce power consumption.

Meanwhile, the demand on data centers continues to grow at an amazing pace.  In June of this year, Cisco Visual Networking Index (VNI) forecasted the annual IP traffic to reach the zettabyte threshold by the end of 2015.  A zettabyte is 2 to the 70th power bytes or 1,024 exabytes. Overall, global IP traffic will increase four times in the next five years.  Sites like Google, YouTube, Facebook and Netflix are driving the growth.  In any case, data centers of the future will have to process more and more Internet traffic, and they will need to do it using far less energy.

Here are a couple of recommendations that could significantly reduce power consumption in data centers.

(1) Use more optical interconnects.  All those server blades in a data center need to be interconnected by a fabric of switches, routers and cabling.  Since the early 90s, when gigabit Ethernet transceivers were introduced, optical transceivers have been used  in data centers, especially for the longer reaches, i.e., 300 meters to 10 km.  Copper transceivers were often used for shorter reaches.  Since the introduction of 10 Gb/s, optical transceivers are increasingly being used for shorter reaches, anything longer than 10 meters.  In 2011, the shipments of 10 Gb/s Ethernet transceivers will surpass 5 million units per year.  Because they consume only one watt of power compared with 10 watts for electrical transceivers, they saved data centers an estimated $170M/year.  If data centers employed optical transceivers on a more widespread scale, they could achieve far more dramatic energy savings.

(2) Use photonic integration and WDM optics to scale to 100 Gb/s and higher speeds.  Following a three-year effort, the IEEE 802.3ba standardized 100 Gb Ethernet links in July, 2010; subsequently, multiple companies announced products supporting  link distances from 100m to 40 km links for data center fabrics.  Unfortunately, some early implementations consume 20 watts of power, or more power per bit than 10 Gb Ethernet solutions. This is because the implementation of the 100 GbE transceiver required 4 wavelengths (4 x 25 Gb/s) in the optical interconnect path, but ten 10-Gb/s paths on the electrical side, increasing the electronic complexity and power consumption.  However, lower power solutions are on the way.  The 10×10 MSA (www.10x10msa.org) supported by Google, Brocade, and more than 20 companies standardized a 10×10 version (10 wavelengths at 10 Gb/s) with implementations having power consumption matching those of 10 Gb/s solutions.

In the future, solutions based upon increased photonic integration, especially silicon photonics, will implement 100 Gb/s with less power per bit than 10 Gb/s solutions.  Silicon photonics solutions integrate low power modulators and detectors and WDM components onto a single chip. Their size, power consumption and performance make them ideal for any data center application from a few meters to 10 km.

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