Inside a data center, servers and networking equipment are securely housed in racks, cabinets, and cages. Because racks and cabinets are often the first pieces of equipment that organizations install, it is crucial to make informed choices to ensure optimal performance.

Data center racks are metal frames used for organizing IT equipment such as servers and switches. Cabinets are enclosed racks that offer added security and environmental control. Cages are secure areas within a data center that house multiple racks or cabinets, providing an extra layer of security.

Navigating the complexities of data center infrastructure can be daunting, but understanding the roles of racks, cabinets, and cages is essential for efficient operations. Dgtl Infra’s comprehensive article explores the purpose, sizing, and costs associated with each of these key components. Keep reading to equip yourself with the insights needed to make informed decisions in optimizing your data center.

Overview: Racks vs. Cabinets vs. Cages in Data Centers

In a data center, racks, cabinets, and cages serve to organize, protect, and manage servers and IT hardware. Additionally, they facilitate cable management and airflow for proper cooling of this hardware. Each feature can be differentiated as follows:

StructureOpen-frameEnclosedEnclosed, often chain-link
Physical FootprintSmallModerateLarge
SecurityLow; minimal protectionModerate; lockableHigh; keycard, biometric access
VentilationHigh; open designModerate; may have fansVaries; depends on design
MobilityModerate; may have wheelsLow; generally fixedFixed; permanent structure
CustomizationLow; highly standardizedModerateHigh; built to specifications

In the sections that follow, we will delve into further detail on data center racks, cabinets, and cages.

Racks in Data Centers

Data center racks are specialized structures designed to hold servers, storage systems, network switches, routers, telecommunications hardware, and other devices. These racks provide not only physical support but also a secure, organized environment that facilitates efficient storage, cooling, power distribution, cable management, and device management. This organized setup streamlines the installation, maintenance, and management of hardware, which is crucial in large data centers housing thousands of servers and network devices.

Data Centers Servers Rack Open-Frame Four-Post Racks

A typical server rack has a sturdy metal frame, constructed from steel or aluminum, which houses multiple slots called “U spaces.” This frame forms the structural foundation of the rack, onto which rails and shelves are attached. These rails and shelves assist in mounting and supporting a variety of IT hardware, such as servers, switches, routers, and storage devices. Shelves can be secured to either two or four posts and come in various designs, including solid, vented, sliding, and fixed options.

Purpose of a Server Rack

The purpose of a server rack encompasses several key functions:

  1. Organization: Server racks neatly arrange IT equipment, streamlining the management of servers, switches, cables, and other hardware. Vertical stacking maximizes floor space utilization
  2. Security: Many server racks have locking mechanisms to offer a physical security layer for the enclosed equipment. These racks comply with rigorous data center security protocols, restricting physical access and often being placed in secure rooms
  3. Cooling: Designed to facilitate airflow, server racks are crucial for maintaining hardware performance and longevity. To optimize airflow and cooling, blanking panels are used to cover unused spaces in the racks, thereby minimizing the chance of hot and cold air mixing
  4. Power Distribution: Server racks usually integrate with, or are compatible with, Power Distribution Units (PDUs). Known as Rack PDUs, these units provide a consistent electrical supply, centralized control, and effective load management for servers and IT equipment
  5. Cable Management: Server racks generally come equipped with cable trays, organizers, and routing aids, which minimize clutter and enhance airflow
  6. Scalability: The modular design, standardized dimensions, and layouts of server racks allows for straightforward expansion. As hardware needs grow, more racks or rack units can be easily added and interconnected together

How Big is a Data Center Rack?

A standard data center rack has dimensions of 19 inches in width, 73.5 inches in height, and 42 inches in depth. However, these dimensions can vary based on the manufacturer and specific requirements.

Datacenter Racks Dimension Sizes Width Height Depth

Here’s a breakdown:

  • Width: The standard width between the mounting rails is 19 inches. However, the overall external width of the rack is typically 24 inches
  • Height: The height is commonly expressed in “rack units” (U), where one U equals 1.75 inches. A standard height of 42U translates to 73.5 inches (42 x 1.75 inches). Floor-standing racks also come in other common heights like 45U (78.75 inches) and 48U (84 inches). Note that the external dimensions may be slightly larger to account for extra space at the top and bottom of the rack
  • Depth: The most common depth is 42 inches, although rack depths can range from 36 to 48 inches to suit different requirements. Additionally, the depth of the mounting rails is often adjustable

The Electronic Industries Alliance (EIA) defined the standard for 19-inch racks through its EIA-310 document. This standard specifies details such as the width of the equipment to be mounted, the size and spacing of the mounting holes, and the height of the rack in rack units (U).

How Many Servers Fit in a Data Center Rack?

A standard 42U rack has space for 42 1U servers when fully filled. The size of each piece of equipment is designated by its form factor, which can vary from 1U to multiple U’s. These form factors indicate the rack space required for each piece of equipment. Total space requirements can be calculated by summing the form factors of all devices.

If space in a 42U rack were to be reserved for a 4U storage array and a 2U switch, then 36U would remain available in the rack for 1U servers. Alternatively, a 42U rack can hold a maximum of 21 2U servers when fully populated. Other common rack sizes, such as 45U and 48U, can hold a maximum of 45 and 48 1U servers, respectively.

Types of Server Racks

Server racks are categorized into four main types: open frame racks, enclosed racks, wall mount racks, and OCP racks. Each type fulfills different data center requirements and configurations.

Open Frame Racks

Open frame racks are the simplest form of server racks, offering unobstructed access to mounted devices. Unlike other types of racks, they lack sides or doors. These racks are constructed from steel or aluminum and are available in two main configurations:

  • 2-Post Racks: These racks have two vertical posts and a single rail. Ideal for lighter IT equipment such as switches and patch panels, they can support weight in the hundreds of pounds range. However, they lack the stability needed for heavy server equipment
  • 4-Post Racks: These racks come with four vertical posts and have both front and back rails. Designed for heavier equipment like servers, these racks can support thousands of pounds. They are more stable and offer better physical protection, particularly for critical network equipment mounted at the rear
Open Frame Servers Rack Two Post Four Post Racks Type

Open frame racks are commonly used in scenarios where airflow control or physical security is not a requirement.

Enclosed Racks

Enclosed server racks have front and rear doors, as well as side panels, making them essentially self-contained 4-post racks. The doors are usually ventilated to ensure efficient airflow from the front of the rack to the back, passing through any equipment that may be installed. These types of racks are also referred to as rack cabinets or server cabinets.

Enclosure Rack Self Contained Four Posts

Enclosed racks provide enhanced security since the doors and side panels are lockable. They also support controlled airflow and offer cable management features. Removable side panels and doors, along with rack-mount rail kits, enable easy equipment installation or removal while still offering protection against unauthorized access. Some models also include noise-dampening features, built-in cooling systems, and the ability to absorb shocks and vibrations. This makes them well-suited for transportation or for use in unstable environments.

Enclosed racks are ideal for high-density data centers and server rooms, as they are designed to accommodate heavier and hotter equipment, as well as higher wattages per rack.

Wall Mount Racks

Designed for compact spaces, wall mount racks attach directly to the wall to hold servers, switches, and patch panels securely. Ideal for small-scale operations, these racks save valuable floor space by eliminating the need for full-size racks or enclosures. Generally, wall mount racks have a height of 12U or less and offer shallower mounting depths than their floor-standing counterparts. Their design often includes a swing-out feature, providing easy access to cables and equipment.

Wall-Mounted Servers Racks Compact Operation

OCP Racks

OCP racks, part of the Open Compute Project, offer a standardized data center rack design focused on efficiency, flexibility, and scalability. Unlike traditional racks, which are 19 inches wide between mounting rails and 42U in height, OCP racks measure 21 inches in width and 48U in height.

Open Compute Project OCP Server Rack Dimensions of 21 Inches 48U
Source: Open Compute Project (OCP).

The design of OCP racks emphasizes modularity and ease of maintenance, as well as efficient power and cooling solutions. A key benefit of this design is that it centralizes power and network connections on the cold aisle side of the equipment, which is the air-conditioned side, simplifying maintenance tasks and improving data center efficiency.

How Much Does a Data Center Rack Cost?

The cost of a data center rack can vary widely depending on the type of rack, its dimensions, the materials used, any specialized features, and the brand. Here are some general guidelines for different types of racks:

Rack TypeOpen Frame RacksEnclosed RacksWall Mount Racks
Cost$100 – $500$500 – $2,000$50 – $500
FeaturesSimple, no enclosuresDoors and side panelsCompact, houses fewer servers

Rack Layout and Elevation

In the effective planning, management, and troubleshooting of a data center, rack layout and elevation are crucial components. Collectively, they contribute to an efficient and well-organized environment.

Rack layout serves as a blueprint that outlines the arrangement of server racks within the data center, in relation to the room, other racks, and key resources like power circuits and cooling systems. This layout helps optimize space utilization, ensures efficient cooling through proper airflow, and facilitates maintenance access.

On the other hand, rack elevation provides an in-depth view of the placement of individual hardware components within a single rack. This is essential for the smooth operation of servers and other equipment, optimizing the use of internal rack space, adhering to the rack’s load capacity – which is the maximum weight the rack can safely support – and enabling easy servicing.

Cabinets in Data Centers

Data center cabinets are enclosed structures designed to house and organize servers and other network equipment. Each cabinet comprises a structural frame, adjustable mounting rails, bracing equipment, grounding studs, interior shelves, and lockable front and rear doors. These doors may be solid, glass, or perforated to offer both security and ventilation.

Data Centre Cabinet Enclosure Front Rear Door

Commonly referred to as “cabs,” these units contain racks and provide a secure, dust-free environment for hardware. They often come equipped with features for cable management, cooling, power distribution, and physical security. Because cabinets are enclosed structures, they may require additional cooling measures if natural airflow is insufficient, such as using fans to enhance airflow and removing obstructions to improve return airflow.

Server cabinets are specifically designed to support both primary and backup power circuits. They can handle circuit capacities ranging from 15 to 100 amps and offer voltage options of 120V or 208V for single-phase power. Additional options for three-phase power and -48VDC for direct current are also common. Power capacity within these cabinets typically varies between 2 and 10 kilowatts (kW).

Purpose of a Data Center Cabinet

A data center cabinet serves many similar purposes to a server rack, such as organizing IT equipment, facilitating efficient airflow and cooling, distributing power, managing cables, and enabling scalable growth. However, unlike server racks, cabinets are enclosed on all sides.

This enclosed design gives cabinets several unique advantages, such as enhanced security and more controlled environmental conditions. Below are specific purposes for using a data center cabinet:

  1. Security: The enclosed design of cabinets offers superior physical security. They often feature lockable doors to deter unauthorized access
  2. Environmental Control: Enclosed cabinets provide more control over internal conditions like temperature and humidity. Some even include integrated cooling systems. They can accommodate both hot and cold aisle containment configurations
  3. High Density: Cabinets are designed for high-density server hosting, with a weight capacity of up to 4,000 pounds. This makes them suitable for hosting blade servers and accelerated computing hardware, such as graphics processing units (GPUs)
  4. Interconnection: Cabinets come equipped with pre-installed copper and fiber optic cables that act as cross-connects to various servers, switches, and other network devices. These cabinets also serve as demarcation points, clearly separating customer-owned networking equipment from the data center’s own infrastructure. This separation simplifies the identification and management of interconnection services
  5. Noise Reduction: The enclosed structure helps to minimize the noise generated by servers and cooling fans, thereby creating a quieter work environment for human operators
  6. Aesthetic Uniformity: With their clean and consistent appearance, cabinets can be particularly beneficial in settings where aesthetics are important, such as in colocation data centers and corporate offices. They neatly conceal equipment and cables for a more organized look

Network Cabinet

A network cabinet in a data center is a secure enclosure specifically designed to hold networking equipment, such as switches and routers, that don’t require significant depth. It safeguards network equipment against physical damage, dust, and temperature changes.

The cabinet features cable management systems for both fiber and copper connections, as well as for power distribution cables. It also includes cooling mechanisms and is designed for the unique airflow patterns of the networking equipment, ensuring optimal performance.

What Size are Data Center Cabinets?

A standard data center cabinet typically measures 24 inches in width, 73.5 inches in height, and 42 inches in depth. However, these dimensions can differ depending on the manufacturer and specific needs.

Datacenter Cabinets Dimension Sizes Width Height Depth

Here’s a breakdown:

  • Width: The industry standard for cabinet width is 24 inches, aligning with the dimensions of removable floor tiles in a raised floor data center. Another common width for cabinets is 30 inches, which accommodates extra-wide enclosures
  • Height: This is often described in terms of “rack units” (U), where one U is equivalent to 1.75 inches. A standard 42U height equals 73.5 inches, which represents the usable interior space for mounting equipment, not the external dimensions. Other common cabinet heights include 45U (78.75 inches) and 48U (84 inches). While a 21U or 24U cabinet is often referred to as a half-cabinet
  • Depth: The most prevalent depth is 42 inches, but this can vary between 36 and 48 inches to meet different needs, such as accommodating deeper servers and blade chassis. Additional depth provides extra space for cabling, Power Distribution Units (PDUs), cable managers, and accessories, without hindering airflow or serviceability

How Many Servers in a Data Center Cabinet?

A standard 42U data center cabinet can theoretically hold 42 1U servers. However, additional hardware such as switches, Power Distribution Units (PDUs), and cable management systems also require space. Additionally, it is essential to allocate room for cooling solutions, either between the servers or as dedicated units within the cabinet. After accounting for these other elements, the actual number of servers that can fit into the cabinet typically ranges from 35 to 40 servers.

How Much Does a Data Center Cabinet Cost?

The cost to purchase a basic data center cabinet starts between $500 and $2,000. However, for cabinets with features such as built-in cooling, biometric locks, and cable management, the price can rise to several thousand dollars.

Rental Costs

In a colocation data center, server cabinets are available for rent in partial (one-half or one-third), full, or multiple configurations. In the United States, rental rates generally range from $1,500 to over $2,500 per cabinet, per month.

Cages in Data Centers

Data center cages are secure, enclosed spaces that house and isolate multiple server racks, cabinets, and other types of equipment. This arrangement further safeguards the servers and networking equipment inside the racks and cabinets. These cages are usually constructed from durable materials like steel mesh or perforated metal panels. In addition to providing strong physical security, they also facilitate effective ventilation to optimize cooling efficiency.

Datacenter Cage Steel Mesh Fence Floor to Ceiling

While company-owned, on-premise data centers may not use cages for their racks, they are a common feature in colocation data centersthese are facilities that manage the data center operations for multiple customers. In such multi-tenant facilities, cages partition the space to allow customers to lease a specific area within the data center. This arrangement enables customers to create fully customizable setups within the secure boundaries of a floor-to-ceiling enclosure.

A cage in a colocation data center can be either private or shared. A private cage contains the IT equipment and servers for a single business, often one that requires highly sensitive data storage. On the other hand, a shared cage accommodates the equipment from multiple companies. Unlike racks and cabinets that rent space by the “U” or “rack unit,” colocation vendors typically rent cage space by the square foot.

Features of Cages in Data Centers

Data center cages have locked gates or doors, with access controlled by a multi-layered physical security system. This may include key cards, biometric authentication, infrared beams, and security guards. Additionally, these cages are usually equipped with surveillance cameras and alarm systems.

To further enhance security, some cages come with mesh or solid ceilings and specialized flooring, effectively sealing off the IT infrastructure from unauthorized access from above and below.

Apart from security, data center cages offer several other key features:

  • Power: These cages can section-off power allocations ranging from several kilowatts (kW) to multiple megawatts (MW). They support both single-phase and three-phase power, as well as primary and redundant power distribution circuits. This makes them well-suited for high-density power and compute applications
  • Cable Management: To organize and route cables efficiently, data center cages utilize a two-tier ladder rack and a fiber raceway, often running overhead. These cable management systems can extend either to the first cabinet in the setup or for up to several feet, depending on the need
  • Interconnection: Many data center cages house a demarcation rack equipped with patch panels. This serves as a centralized boundary point for managing cross-connects between different organizations or service providers. This demarcation point utilizes the existing ladder racks and fiber raceways for organized interconnections

Purpose of a Data Center Cage

Data center cages serve multiple important purposes such as enhancing security, allowing customization, providing isolation, and facilitating resource sharing.

Cage Security Separation of Collocation Datacenter Spaces
  1. Security: The primary role of a data center cage is to restrict unauthorized access to servers and networking equipment. It ensures that only authorized personnel can access this hardware for maintenance, upgrades, or other essential activities. Limiting access also minimizes the risk of both accidental and intentional physical damage to the hardware
  2. Customization: These cages offer a high degree of customization. They come in various sizes, from small enclosures for a few servers to large, custom-built structures that can house extensive hardware configurations and multiple cabinets. Additional features such as Power Distribution Units (PDUs), specialized cabling, and cooling fans can also be included to meet specific hardware requirements
  3. Isolation: Data center cages provide organizations with a dedicated and isolated space for their hardware. This is crucial for entities that must adhere to strict compliance standards, such as HIPAA in healthcare or GDPR in the European Union
  4. Resource Sharing: For businesses that don’t require an entire data center but still need robust infrastructure, data center cages allow them to benefit from the resources of a larger facility. This includes power, cooling, and security, without the need for building and maintaining their own data center

What Size are Data Center Cages?

Data center cages typically range in size from 100 to over 5,000 square feet, with fencing that can reach a height of 9 feet. Generally, these cages allocate around 20 square feet for each cabinet position. They are also designed to handle high-density deployments, supporting up to 300 to 1,000 watts per square foot. Artificial intelligence workloads are a prime example of applications that require this high power density in data centers.

Frequently Asked Questions (FAQ)

What is a Rack vs Cabinet in a Data Center?

A rack and a cabinet, also known as an enclosure, in a data center serve related but slightly different purposes. A rack is a metal frame designed to hold various hardware devices such as servers, switches, and other networking equipment. On the other hand, a cabinet is essentially a rack enclosed by walls, doors, and a top, offering additional security and protection for the equipment stored within it. While racks are more open and provide easier access, cabinets offer better environmental control and physical security from unauthorized access.

What is a Rack vs Cage in a Data Center?

A rack in a data center is a standardized frame for mounting multiple hardware modules, such as servers, storage units, and networking equipment. A cage, on the other hand, is a secured, enclosed area within a data center that contains one or more racks and offers an extra layer of security and isolation. While racks are used to organize and hold hardware, cages are used to separate and secure the racks, cabinets, and equipment of different customers or projects.

What is Rack Space in a Data Center?

Rack space in a data center refers to the physical area designated for housing servers, storage, networking equipment, and other hardware within a standard 19-inch wide rack. These racks are typically organized in rows and may be secured in cabinets for added security and better cable management. The amount of rack space available is often measured in “U” or “rack units”, where one U equals 1.75 inches, representing the vertical space that a device occupies.

How Many Racks are in a Typical Data Center?

The number of racks in a data center varies significantly based on the facility’s size, purpose, and design. A small enterprise data center may have only 5 to 10 racks, while a medium-sized facility could contain between 50 and 100 racks. In contrast, large hyperscale data centers operated by cloud service providers can house several hundred or even thousands of racks.

Why is IT Called Rack and Stack?

The term “rack and stack” in Information Technology (IT) is the process of mounting servers, network devices, or other hardware into a rack and then stacking them in an organized manner. The word “rack” signifies the frame or enclosure that holds these devices, while “stack” indicates the orderly arrangement of these units one above the other within the rack. The phrase encapsulates the idea of efficiently organizing and installing hardware components in a data center or server room.

What is the Difference Between a Rack and a Tower Server?

A rack server is designed to be mounted within a standard 19-inch rack framework, allowing for efficient use of space by stacking multiple servers on top of each other. In contrast, a tower server is a standalone unit that resembles a traditional desktop computer, taking up more physical space and generally not designed for stacking. Rack servers are typically more suitable for data centers and larger businesses with multiple servers, while tower servers are often used in smaller environments, like the office of a small business, where fewer servers are needed.

What is the Difference Between a Network and Server Cabinet?

A network cabinet is generally used to house networking equipment such as switches, routers, and patch panels. It facilitates cable management and airflow for devices that don’t require significant depth. A server cabinet, on the other hand, is designed to hold servers and is usually deeper to accommodate the larger size and heat output of server equipment. Both types of cabinets aim to organize and protect equipment but are tailored to the specific needs of either networking hardware or servers.

Mary Zhang covers Data Centers for Dgtl Infra, including Equinix (NASDAQ: EQIX), Digital Realty (NYSE: DLR), CyrusOne, CoreSite Realty, QTS Realty, Switch Inc, Iron Mountain (NYSE: IRM), Cyxtera (NASDAQ: CYXT), and many more. Within Data Centers, Mary focuses on the sub-sectors of hyperscale, enterprise / colocation, cloud service providers, and edge computing. Mary has over 5 years of experience in research and writing for Data Centers.


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