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20th Jun 2008

Blade Servers – Data Centre Environments to Support This New Approach

The server has traditionally been a fairly stable and predictable technology as the foundation for most organisations. As such, rapid and unpredictable change isn't a positive. Yet the most welcome and potentially most advantageous technology change is the blade or high density environment. The ability to scale more quickly and have hot-swappable resources to prevent downtime is very attractive.

Heat Density at the Rack Level is the Issue
The main issue for most users is how to deal with the very localised heat and cooling problems that are likely to occur with many server blades in a single, fairly dense space. Though high density is part of the design that provides so many benefits, it also creates a very substantial "hot spot" in the data centre. Traditional data centre cooling approaches of just chilling the ambient air don't provide enough cold air in a predictable manner where it's needed most: at the front of the rack.

Many customers utilise only 20-30% of their blade servers. In most cases, fan assisted room air is enough to keep things cool and running. However, as blades are added, heat problems start to become more likely as the localized heat in the blade server increases.

Raised floors are also a very limited solution. First, the amount of cooling air needed is often at the extreme limit of what raised floor systems can provide.
Second, there is an issue of what to do with the exhaust air. This can't be just dumped into the room; rather, it needs to be removed. The best course of action is to prepare a blade server implementation for a full rack, with the requisite cooling from the onset.

New Approaches to Cooling
The blade environment has three key requirements to run at high levels of availability and to prevent heat issues from compromising performance:
• Requisite local cooling
• Ability to generate substantial airflow to the rack
• Ability to remove hot air effectively

One of the most successful approaches of cooling dense racks is the use of the "enclosed hot aisle/cold aisle" design approach.

This approach creates a closed environment where the hot air that comes from the back of the server rack is contained in an "aisle". The hot exhaust air is then ducted into air conditioners that reject the heat from the data centre. This closed system prevents the mixing of hot exhaust air and cooling air. The hot aisle/cold aisle rack environment is self-contained, and may be installed within existing data centres. It can also support expansion without disruption of data centre operations.

Conclusion
Today's generation of blade server products offer very real and significant benefits. However, there are new and substantially different environmental considerations that need to be put in place to fully utilise the technology. Moving to an enclosed hot aisle/cold aisle design is a best practice optimised for blade servers and provides an environment allowing seamless transition from a marginally populated blade server to a fully populated one.

Source: Aaron Goldberg, www.apc.com, 2008