Q

Cooling in the blade rack

Blade servers may help to reduce the footprint I take, but how can I be sure of cooling in the rack? What sort of rack should I look for? And why?

Blade servers may help to reduce the footprint I take, but how can I be sure of cooling in the rack? What sort of rack should I look for? And why?
That statement may not actually be true, depending on the number of servers you utilize, although it is true to some extent. I say that because at this point you cannot fill a rack with blade servers and cool them all in time. However, new liquid cooled racks are on the market to assist in increasing the number of chassis that you can use in each rack. Rittal has one. APC and Liebert also have products to address both new installations and retrofit situations. Before I go any further, let me say one thing -- I have heard that some vendors are telling their end users that using someone else's cabinets will void their warranty. BUNK! If you look at the warranty, it only stipulates operating temperature so beware of this one.

That said, you have several options for cooling: natural air, forced air, a combination of both and liquid cooling.

People tend to freak out about having liquid cooling in their data center, but if you have a sprinkler system, you already have water in the data center (food for thought). In planning your cooling, you will require one thermal unit of cooling for each KW of power you consume. Here are a few schools of thought to consider:

  1. Get rid of the abandoned cable under the floor. This is the biggest hurdle to cooling efficiency in many data centers. You can't push air through a wad of cables. By the way, this is also now a code requirement (NEC 2005). An air study will also help. APC has a program to do this (don't worry -- not vendor specific).

  2. In an natural air flow system, you can increase cooling efficiency by making sure that you have some means to deal with the heated air -- either pull it out of the room, use a very high ceiling to help it dissipate or duct it out of the room.

  3. With forced air or with a combination of forced and natural air, you assist the cooling by utilizing fans to draw the cool air into the cabinets. A good rule of thumb is to allow two perforated tiles (4') in front of your cabinets. Make sure that any places the cold air can escape (though holes in the floor, blank areas in cabinets, etc.) are stopped with brushes and blanking panels. This improves efficiency.

  4. Liquid-cooled cabinets provide sort of a personal chilling unit for the enclosed equipment. They are connected to your water pipes and in some cases to a water tank. Many buildings have underutilized chiller units, which can be incorporated into the system.
Your best bet is to look at your system now. Check your efficiency and see what additional capacity you can support. Then size your new requirements. I hate to get into a situation where any one manufacturer is recommended over another, since I work with them all. And all have great solutions to this problem. Just make sure you are not overbuying. I would also recommend that you go to another data center where the products are in use. Also chat with an end user or two to determine how happy they are with the solution and get a realistic expectation of day two costs. And finally, in case I haven't written enough already -- an onsite visit will let you get a feel for the noise level of the equipment. Some of this stuff is really, really loud!
This was first published in March 2006

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