The following excerpt from Datacate’s Colocation Survival Guide discusses the steps required to accurately determine colocation space requirements, taking into consideration not only equipment but also constraints that may be imposed by the data center. Get the full Colocation Survival Guide here.

How much space in the data center will your colocation require? This will primarily be determined by:

• the equipment set that you plan to install;
• any minimum space allocation requirements imposed by your provider;
• any legal or regulatory requirements that may apply to your business or the application to be hosted by your colocation.

In the data center, space is typically measured in standard cabinet/rack units, called “U”. A 1U space is equal to the usable width of the cabinet or rack (=< 19 inches), the usable depth of the cabinet (varies from 30 inches to 42 inches, 36 inches is common), and a vertical allocation that is exactly 1.75 inches high. The width and depth dimensions are constants, so you get more overall space by going vertical, i.e.: 2U = W x D x 3.5”, 4U = W x D x 7”, etc.

ADDING UP YOUR U’S

Servers and other equipment that is specifically designed for data center rack or cabinet deployment will conform to the U form factor, and so you’ll typically see servers and other devices described by their U size, i.e. a 1U network switch, a 2U server, etc. This makes determining your minimum space requirements easy: just add up the U factors for all of your equipment. If you have two 4U servers, three 1U servers and a 1U switch, you’ll need no less than 12U for your colocation (you may need more if you are installing a PDU or other ancillary equipment).

What if some or all your equipment is not designed for rack-mount applications? Examples would include tower or desktop servers, desktop external drives and desktop network appliances? In those cases, you’ll need to grab a tape measure and do some figuring on your own, keeping in mind the usable width and depth available to you, and that standard cabinet U height. If you have a tower server that is 17” high or less, you can lay it on its side to better conform to cabinet/rack space distribution; the server will fit in a 4U-5U space. With all non-rack-mount equipment, you will need to plan for a data cabinet shelf, which will support the equipment and will typically consume a U by itself.

MEETING MINIMUMS

Some providers will have a minimum amount of space that you must take, whether or not you need it, so inquire as that will factor into your total cost. Also, if your colocation will be used to host electronic Protected Health Information (e-PHI), payment information such as credit card numbers or bank account numbers, or any other information that is considered sensitive or is governed by privacy laws or industry rules (HIPAA, PCI DSS), you must install your colocation in a private locking space with controlled access. That then becomes the determinate of the minimum space you must purchase, as private locking spaces are typically ½ cabinet (20U) in size, though a few providers do offer smaller locking spaces. Finally, if your colocation is large enough that it could occupy several full racks or cabinets, the provider may suggest that you consider a private cage. Cage space is sold by the square foot, with 80 – 100 square feet typically being the minimum. In addition to the space, the provider would provision multiple power circuits, network drop(s), and may supply racks or cabinets within the cage for your equipment (sometimes you have the option of providing these yourself).

TIP: Any decent modern data cabinet will be outfitted with both front and rear vertical post pairs for mounting of equipment. Shallow-depth devices, like network appliances, horizontal PDUs and even some smaller servers, can be mounted in a back-to-back configuration: one device mounted on the front posts, the other mounted directly behind it on the rear posts. In this way, two devices can share the same U, reducing your overall space requirements.