What are server rack slots?

Slots in a server rack are called U spaces. Three holes equals one U space. Each U space is 1.75 inches total.

Understanding Server Rack Needs Based on Units

June 19, 2014
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If you are new to the world of servers and server racks, you are not alone; you might need a primer to bring you up to speed on some of the specific terminology and jargon that you will encounter in your server rack searching adventures. Never fear. You will soon understand and feel comfortable discussing your server needs with professionals in the industry without a tinge of self-consciousness.

One critical part of searching for your new server rack is understanding what professionals and industry experts mean when discussing rack units.

You might hear someone mention a “rack unit” or a rack “U” or “RU” and wonder what that means. The “U” actually stands for the vertical measure of a server rack. Basically, a rack unit comprises the height of a server rack with a 19-inch or 23-inch height. Since a typical full-sized rack comes in at 4U, the 2U rack servers and 1U rack servers are considered half-rack servers.

One rack unit actually measures at 1.75-inches and each unit is the standard measure for available usable space in each server rack. The unit is actually the space between each shelf where you can place equipment for your server needs, which means that, for each slot, you can place anything that fits within the 1.75 inches in height that is available per slot. A solid example of this sizing and definition is when you look at a 44U server rack. With this size rack, you have 77-inches of usable space available since you multiply 44 by 1.75 and arrive at 77.

If you are a data center manager and need to calculate your needs for the number of rack units you need, you need to look at your projected storage needs from your server racks. Calculate for your internal storage needs; so if you anticipate that you will need 20 2U rack servers in the next few years, you might consider buying a 44U rack enclosure.

As you work with rack servers, you will understand the language much better, and it will feel like second nature to you when it comes time to purchase more equipment.