What is colocation by the U?

While giving a walking tour of our Chicago data center recently, I mentioned that the cabinets on our left were “colo by the U”. When I was met with a confused look, I soon realized that my guest had no idea what I was talking about. While most people understand that colocation is simply renting data center space for your equipment, there are actually three varieties:


– Cage (or room)

Renting an entire room in a data center (affectionately known as a “cage” due to it’s fence-like walls). The customer is typically responsible for providing their own routing and switching hardware.


– Cabinet (or rack)

Renting a refrigerator sized server cabinet that can accommodate approximately 40 servers (racks are just open cabinets). The provider typically provides routing, but the customer is often responsible for providing their own switching hardware. This is a typically a good option if you have more than 10 servers, and are looking for the flexibility to add or remove servers.


– By the U (or single server)

Renting space for one or more servers in a cabinet. While all modern rackmount servers are 19″ wide, they can vary significantly in height. Cabinet space is measured vertically in “Rack Units”, abbreviated simply to “U” (each “U” is 1.75″ tall). When you choose colocation “by the U”, you are simply renting a part of a cabinet for your equipment. If you add more machines, simply purchase more space. Each server will need a power outlet and network connection, so make sure the plan you select has enough of each. This is a good option if you have less than 10 servers. The provider typically provides both routing and switching, so setup does not require specialized networking experience.