When you are working in a data center, you might all have heard the word racks and cabinets. Are these are same or is there any difference between both? What would be the industry standard to define its size and shape? Let’s have a look at these concepts in detail.

A rack is an open frame designed for mounting multiple electronic equipment modules to hold servers and IT equipment(typically with rails, bars, hooks, or pegs).

Cabinets are like racks in that they can hold multiple modules for electronic equipment. The main difference between a cabinet and a rack is that racks are open and have no sidewalls, while cabinets are enclosed on all sides including front and rear doors, side panels, and a roof. Do understand that the cabinets are also known as closed frame racks.

We can say that the backbone of any cabinet is a rack itself. Does that simple explanation and pictures answer your question? So which one should I use? In order to answer that you have to understand the advantages of both as below,

Despite the latest trend towards using enclosed cabinets, open frame racks still present a perfectly viable solution for many data center deployments. Benefits include:

• Addresses a variety of applications, from supporting active equipment such as switches and servers to providing a cable patching platform.
• It provides unobstructed airflow.
• Creates easy access to equipment and cabling sections, reducing maintenance time for moves, additions or changes.
• Provides the ability to use wide and deep vertical cable managers along both sides, offering the perfect cable management solution
• Costs less than enclosed cabinet solutions

However, there come some drawbacks:

• Easy access can create a security concern for potential damage
• Active equipment is exposed to contaminants (dirt, debris)
• Exposed cables and cable managers can lead to poor aesthetics, especially if poorly maintained

When we consider the cabinets those are having a popularity for two major reasons:

• It offers the best and simplest approach to a variety of air segregation strategies, including Cold Aisle Containment, Hot Aisle Containment, and cabinet-level containment. If you have read my previous article you might understand the importance of different cooling strategies and it’s criticality in the data center.
• Includes much higher physical security levels, with different types of locking systems available to enhance protection from unauthorized entry.

Because of these two critical advantages, cabinets are more used in data centers.

Despite these advantages, enclosed cabinets have a couple of challenges:

• Higher administrative headaches for installation and maintenance due to enclosed structure and restricted accessibility.
• Higher costs may prohibit data centers, especially small operations or start-ups.

The simplest form of differentiation we can say that racks and cabinets are used to fulfill the same function and slightly differ only in design. Because of this, people often refer to the rack as a cabinet and cabinet as a rack too. Which we can’t deny. It’s important to consider all the factors that will play a major role in your project and choose the solution that will best serve the core requirements.

Size of a cabinet

Cabinets vary greatly in shape and size and are commonly defined by the width and depth in millimeters e.g. 800mm x 1000mm, with the height being specified in rack units e.g. 42U.

A rack unit is the smallest measurement of data center space, typically referred to as “U” or “RU” (Rack Unit) is a measurement of height. EIA-310 defines the Rack Unit (U) to be the usable vertical space for a piece of rack mounted equipment. This is used to measure the height of a server rack, one “U” is 1.75 inches high. One “U” represents one slice of rack or cabinet space. The width and depth of standard data center racks will slightly vary by manufacturer, but the industry standard is 19 inches wide and 36 inches deep. This is the outer dimension of the equipment mounting rail and is common to most cabinets today. Manufacturers specify their equipment as being “19” rack-mountable”.

A server rack or cabinet rack measuring around 20U or 24U is considered a standard half rack or half cabinet, while a 42U server rack or cabinet is the standard full-size rack or full cabinet.

Physical size

• Width dimensions will vary based on the need to manage cables, patch cords and airflow
• Depth is mostly dependent on the intended use and dimensions of equipment to be installed
• Height choice of size is based on functionality and equipment loading, the physical limitation being the floor to ceiling height. Data Center designers drive the demand for increased RU capacity with 47U and 52U gaining popularity.

Cabinet Usage Strategy in the data center

The cabinet usage strategy is principally determined by the type of data center, for example:

• The enterprise data center is owned and used by a single organization. The strategy for the use of cabinet space is an internal decision, focused solely on the need of the enterprise.

In this situation, a more holistic view of floorspace planning can be taken to maximize equipment capacity.

• Owners of colo data centers will be leasing space to outside agencies and will have to factor in segregation due to data sensitivity and security requirements.

In this situation, it is likely to be the customer who specifies cabinet functionality and design.

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