Why cooling your rack switch shouldn't be complicated

Why cooling your rack switch shouldn't be complicated

Are your ToR switches being cooled properly?

Gone are the days when top-of-rack (ToR) network switches were considered luxurious. Today, an increasing number of data center managers are relying on ToR switches for three primary reasons:

  1. Significant reduction in cable quantities.
  2. Lower network infrastructure costs. 
  3. ToR switches are now built to handle higher-density loads. 

Top-of-rack switches, as suggested by the name, involve storage of the network switch at the top of the rack. This contrasts with the end-of-row switch setup. Under that model, cabinets were flanked by rack switches, which required running more cable and, ultimately, more infrastructure in the form of extra racks. 

The benefits of ToR switches may be evident, but they come with a unique caveat, which is that they're more difficult to cool for several key reasons. This post dives into those complications, and offers a simple but effective way out of them. 

Understanding the dilemma 

There are three main complications with placing network switches at the top of the rack. 

  1. This is the hottest part of the rack since it's farthest from the cool-air source.  
  2. The air intake of a given network device can vary from side-to-side, front-to-rear or rear-to-front.
  3. All cables lead to the ToR switch, which increases the risk of stifled airflow. 

The first item on this list is problematic because it increases the likelihood that warm air will re-circulate through the rack due to the lack of air pressure. As a result, not enough cool air will be present to reduce the temperature of the switch. This is called bypass airflow, and it's one of the primary reasons cooling infrastructure fails.

The second item is also technically a form of bypass airflow, but for a different reason. According to TechTarget contributor Robert McFarlane, technicians will typically mount a switch backward to keep connectors in the rear of the cabinet. This means the intake fan may actually face the hot aisle. In other cases, network switches will have side-to-side airflow. This can also limit the amount of cool air that reaches the switch.

Finally, with so many cables plugged into the switch, there is an increased risk of stifled airflow. If hot air is not adequately dispelled, the switch can overheat.

The result of any of the above problems is the potential for downtime for that switch. And when the switch goes down in a ToR setup, the entire rack goes with it.

An overheating ToR network switch is a sure recipe for downtime.An overheating ToR network switch is a sure recipe for downtime.

The fix: Airflow management for ToR switches

"ToR switch cooling doesn't have to feel like pulling teeth."

Zooming out, all of the cooling problems associated with ToR switch placement stem in some way from airflow management. As with servers, cool air must constantly flow into the device, and hot air must be expelled as exhaust. The question is, how can this be achieved with so many variables simultaneously influencing rack-switch cooling? The answer is a lot simpler than you might have thought.

"ToR hardware is now available that maintains front-to-back cooling while leaving the connections where the technicians want them," McFarlane wrote. "In high-density installations, this is the only way to go."

The hardware McFarlane speaks of works like this: A barrier placed in front of the switch ensures that only cool air can enter the equipment's intake. Exhaust – regardless of the switches' orientation – is directed away from the air intake. This passive system effectively ensures that distance from the cool-air source, the direction of the intake valve and, to an extent, the concentration of cables will not inhibit the ability of hot air to escape the rack. 

With the right airflow management tool, ToR switch cooling doesn't have to feel like pulling teeth. Click here to see just how easy it can be.