What Is a Server Rack: Specifications, Usage, History, and More

This Whitepaper answers “What is a server rack?” in detail, providing an overview of their function, infrastructure dimensions, standardization and history.

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A server rack is a standardized, vertical frame designed to securely house and organize multiple servers, networking equipment, and other IT hardware in data centers or server rooms. 

Its significance in the IT world lies in providing a centralized, space-efficient solution for managing and maintaining crucial computing resources. 

This whitepaper will delve into the critical components of a server rack and its benefits in terms of space optimization, cooling, and ease of maintenance. We’ll explore how server racks enable seamless scalability and data center management, making them indispensable tools for modern businesses reliant on robust IT infrastructure.

Well-lit rows of server rack cabinets in a data center

What Is a Server Rack: Server Rack Basics (Anatomy)

As stated above, a server rack is a fundamental component in data centers and IT environments, serving as a centralized housing system for various computing equipment. Here are the essential parts of a standard server rack.

Server Rack Components

Frame: The frame forms the main structure of the server rack, providing a sturdy foundation to hold all the components securely in place.

Rack Units (U): The server rack’s height is measured in rack units (U), where one U is equal to 1.75 inches (44.45 mm). Servers and other devices are designed to fit into specific U-sized slots within the rack.

Rails: These horizontal bars run along the sides of the server rack, facilitating easy sliding and mounting of equipment.

Cage Nuts and Screws: These are the primary fasteners to secure servers and other devices to the vertical posts of the rack.

Cooling Mechanisms: Server racks often feature built-in cooling systems, such as fans and air vents (typically located at the top), to regulate and dissipate heat the enclosed equipment generates.

Power Distribution Units (PDUs): These units manage power distribution to the devices within the rack, helping to avoid power overload and providing remote power control. Some more modern server racks come with built-in uninterruptible power supply (UPS).

Cable Management: Cable organizers and management arms keep the cables within the rack neat and organized, ensuring easy maintenance and minimizing airflow obstruction. 

Blank Panels: These fillers cover unused rack space, promoting proper airflow and maintaining a clean and organized appearance.

Front and Rear Doors: Nowadays, server racks typically have front and rear doors with locks for security.

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Server rack typical components

Standard Server Rack Sizes and Form Factors

Server racks come in various standard sizes and form factors, allowing organizations to choose the best fit for their specific needs and available space. Here are some common standard server rack sizes and form factors:

Server Rack Width

A 19-inch rack is a standardized frame for housing electronic equipment modules in diverse fields like datacom, telecommunications, audiovisual production, scientific research, and networking hardware. 

The term “19-inch” server rack is sometimes used to refer to the entire rack. However, it only refers to the width of the front panels installed in the rack. These racks also come in 23-inch and 24-inch versions (not so common) based on hole-to-hole spacing (rail-to-rail).

To summarize, these are the three standardized widths used today by most data centers: 

Server Rack Height

The Electronic Industries Alliance (EIA), a former association of US electronic manufacturers, introduced the EIA-310-D standard that provides guidelines for rack components. 

The Rack Units (U) determine the vertical spacing, with 1U equaling 1.75 or 1 3/4 inches (44.45 mm). Vertical hole spacing follows a repeating pattern of holes within 1U. 

Horizontal spacing of vertical rows is generally 18 5/16 inches (465.1 mm), but it can vary, so manufacturers often use adjustable mounting slots. The rack opening must be at least 17 3/4 inches (450 mm) wide, while the front panel width remains a standard 19 inches (482.6 mm), though the actual rack width may differ depending on the design. 

EIA-310-D Standard dimension for one rack unit

Server Rack Classification (Based on Height)

The height of a server rack is measured in rack units (U). Based on this labeling system, server racks are classified by this height, like “48U server racks” or, more casually, “7-foot racks.”

Typically, large data centers use “full racks”:

  • 42U
  • 48U

However, there are a plethora of options for organizations to choose from. Most manufacturers offer “half-racks,” which are 22U and 27U. There are also 6U, 10U, 12U, and many more designed for personal use or smaller organizations or startups. 

Some server rack manufacturers offer non-standard sizes, especially with open-frame racks. These racks can be as tall as 70U or as small as 5U. Enclosed server rack cabinets might have non-standard sizes as well, like 18U or 37U.

While these standards exist, compliance isn’t enforced since no governing body oversees them anymore.

Server Rack Depth

The last crucial aspect of server rack dimensions is the depth, which refers to the distance between the front and back rails of the rack. Depths can vary significantly, ranging from a few inches to over 50 inches. The most commonly standardized depth dimensions for server racks are as follows:

  • 27 inches
  • 31 inches
  • 37 inches
  • 42 inches

Keep in mind that these measurements represent the actual depths. The usable depth where the devices are installed is slightly less. It’s best practice to purchase a server rack with generous depth to avoid installing devices that won’t fit. However, modern server rack enclosures come with adjustable rails, allowing flexibility. 

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Common Server Rack Features

Weight Limits and Load Distribution 

One of the crucial aspects when considering a server rack is its weight capacity and load distribution capabilities. Each rack has specified weight limits, indicating the maximum amount of equipment it can safely hold. Overloading the rack can lead to structural instability and potential equipment damage. Following the manufacturer’s guidelines and avoiding exceeding the recommended weight capacity is imperative.

Moreover, proper load distribution within the rack is vital to maintain stability. Equipment should be evenly distributed across all mounting points to avoid excessive strain on specific areas. Heavier devices should be placed at the bottom of the rack to maintain a low center of gravity and prevent toppling.

Most 48U server racks can hold about 3,000 pounds or 1,365 kilograms for static load and 2,250 pounds or 1,025 kilograms for dynamic load.

Cooling and Airflow Considerations 

Efficient cooling and proper airflow management are critical to maintaining optimal operating conditions for servers and networking equipment. Server racks often feature cooling mechanisms like built-in fans, ventilation holes, or perforated doors. These elements facilitate the flow of cool air into the rack and the expulsion of hot air generated by the enclosed devices.

Cable management also plays a crucial role in maintaining airflow. Properly organized and routed cables prevent blockages and ensure smooth airflow throughout the rack. Some server racks have cable management panels, trays, or channels to keep wires neat and organized, reducing the risk of overheating caused by restricted airflow.

Rack Security Features 

Server racks house valuable and sensitive equipment, making security a top priority. Many server racks have lockable front and rear doors to restrict access to unauthorized personnel, preventing tampering or theft.

Additionally, some racks have removable side panels with lockable options, enhancing physical security. Advanced security features may include biometric access controls or intelligent card systems, adding an extra layer of protection to safeguard critical IT assets. Properly securing the server rack ensures the integrity and availability of the equipment and the data it contains.

Common Server Rack Types

Each type of server rack offers distinct advantages and is chosen based on factors like available space, equipment, security requirements, and scalability. Whether it’s the cost-efficient open-frame rack, the secure and versatile cabinet rack, or the space-saving wall-mount rack, selecting the appropriate server rack type ensures efficient organization, protection, and optimal performance of critical IT infrastructure.

Open-Frame Server Racks

Open-frame server racks, sometimes known as “two-post racks,” feature a minimalist design with two vertical posts and two or four horizontal bars for equipment mounting. These racks provide easy access to equipment from all sides and are commonly used for network switches, patch panels, and lightweight servers. Their open structure allows for excellent airflow and efficient cable management. 

Open-frame racks are popular in data centers, telecommunications rooms, and server closets, especially when cost-effectiveness and easy equipment installation are essential considerations. However, they may not offer the same physical security and protection as enclosed cabinets.

Cabinet Server Racks (Enclosed Server Racks)

Cabinet server racks, also called enclosed server racks or 4-post racks, provide fully enclosed and secure housing for sensitive and critical IT equipment. These racks comprise four vertical posts and removable side panels and doors, offering robust protection against physical access and environmental factors. Cabinet racks are available in various sizes, accommodating small office setups to large data center installations. 

They are designed to house multiple servers, networking gear, storage devices, and other equipment. Many cabinet racks have advanced features such as cable management options, cooling systems with fans and vents, and power distribution units (PDUs) provisions to streamline equipment organization and maintenance. The enclosed structure ensures enhanced security, reduced dust accumulation, and better control over temperature and airflow. However, they are significantly more expensive than the latter.

Wall-Mount Server Racks

Wall-mount server racks are space-saving solutions designed to be affixed to walls, making them ideal for environments with limited floor space, such as small offices or remote locations. These racks come in various sizes and configurations, allowing organizations to mount network switches, patch panels, and shallow-depth equipment vertically on the wall. 

Wall-mount racks may feature swing-out or hinged options, providing easy access to the equipment during installation and maintenance. While they have a smaller capacity than full-size cabinets, wall-mount racks are practical choices for housing essential network equipment in confined areas. They help keep the floor clear, maximizing the available space and enabling convenient cable management.

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WHITEPAPER – Optimizing Server Cabinet Rack Space to Maximize Efficiency and Reduce Costs

Optimizing Server Cabinet Rack Space to Maximize Efficiency and Reduce Costs FREE Guide - AnD Cable Products

Smart optimization can help you increase rack space and realize significant equipment cost savings. Read our step-by-step guide that shows you how – and how much you could save.

  • How Much Rack Space You Could Save
  • How to Optimize for Maximum Efficiency
  • Savings for New and Retrofit Installations
  • Overall Cost and Space Savings Post-Optimization

Server Scalability and Other Considerations

Organizations can design a well-optimized and future-ready server rack infrastructure by carefully addressing scalability, cable management, cooling, and device installation considerations. 

Scalability and Future-Proofing

When planning a server rack infrastructure, scalability is a paramount consideration. A scalable setup allows organizations to accommodate future growth and technology advancements without significant redesigns or costly overhauls. 

Choosing a server rack that offers expandability, such as opting for a large server rack (48U), ensures that future upgrades do not require buying a new server rack. This will allow for easy integration of new equipment as the business expands. 

Future-proofing involves considering the latest standards and technologies to support emerging hardware and connectivity requirements. A scalable server rack setup enables businesses to stay agile and adapt to changing IT demands without disruption.

Cable Management and Accessibility

Efficient cable management is essential for maintaining a well-organized and tidy server rack setup. Properly routed and labeled cables help prevent tangling, reduce the risk of accidental disconnections, and simplify troubleshooting and maintenance. 

Server racks with integrated cable management features, such as cable trays, routing channels, and cable ties, streamline cable organization and improve airflow for efficient cooling. Additionally, easy accessibility to equipment is crucial for swift installations, repairs, and upgrades. 

Cooling and Energy Efficiency

Cooling is critical in maintaining optimal operating conditions for servers and networking equipment. Overheating can lead to hardware failures and performance issues. Server racks equipped with efficient cooling mechanisms, such as built-in fans, airflow optimization designs, and hot-aisle/cold-aisle containment systems, help regulate temperature and dissipate heat effectively. 

Energy-efficient server racks, combined with power-saving features like variable-speed fans and intelligent power distribution, contribute to reduced energy consumption and lower operational costs. By optimizing cooling and energy efficiency, organizations can create a sustainable and environmentally friendly data center environment.

Device Installation and Maintenance

Simplified device installation and maintenance processes enhance overall rack usability. Server racks with tool-less installation options, adjustable mounting rails, and clear equipment labeling ease the setup of new hardware and reduce installation time. 

Quick-release side panels and easy-to-remove doors facilitate swift access to internal components for routine maintenance and repairs. Moreover, considering the weight of the installed equipment is vital, as some server racks come with load-bearing limits that dictate how much hardware can be safely housed. 

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Server Rack History

Early Data Storage and Organization Methods

In the early days of computing, data storage, and organization were relatively simple compared to modern standards. Electronic equipment, such as mainframe computers and early servers, were often housed in large, custom-built cabinets or enclosures. 

These cabinets lacked standardized sizes and were cumbersome to maintain. As computing technology evolved and the need for more efficient data storage solutions grew, the concept of standardized server racks emerged.

Development of Standardized Rack Systems

In the 1980s, the electronics industry recognized the need for a more efficient and organized way to house computing equipment. The Electronic Industries Association (EIA) played a pivotal role in establishing the first standardized rack system in the form of the EIA-310 specification. This specification defined the Rack Unit (U) as a standard vertical measurement, with each U equaling 1.75 inches (44.45 mm). The EIA-310 standard laid the foundation for modern server racks, allowing for uniformity in size and compatibility among various server and networking hardware.

The 19-Inch Server Rack Origin

The 19-inch rack format, with standardized rack units of 1.75 inches (44.45 mm) each, was introduced by AT&T in 1922 to optimize space in telephone central offices. 

There were already two-post racks as early as 1911, and they were more recognized as relay racks in the world of telephony. However, there was little evidence showing standardization. It was only in 1934 that the EIA established the 19-inch rack standard. In 1992, the EIA standard was revised to align with the 1988 public law 100-418, setting the standard Rack Unit (U) measurement as 44.45 millimeters (1.75 inches). Each U is calculated as 15.875 mm (0.625 in) + 15.875 mm (0.625 in) + 12.7 mm (0.500 in).

Over time, the one introduced by AT&T became the rack standard and is widely adopted in various industries, including telecommunications, computing, audio, video, and entertainment. 

Today, the 19-inch rack arrangement is prevalent in data centers, ISP facilities, and corporate server rooms due to its ability to accommodate dense hardware configurations while minimizing floor space.

Server Rack Accessories and Add-ons

Standard server racks can accommodate various cable managers and organizers. These accessories are crucial to maintaining a clean and organized server rack setup. They come in many forms, from cable trays to rings or ties. 

Proper cable management not only improves the overall appearance of the rack but also enhances airflow, ensuring effective cooling and reducing the risk of cable-related issues.

AnD Cable Products Horizontal Zero U RackOrganizer®

One of the most innovative cable managers today are the ones that not only keep server cables clean but also offer significant cost and space savings to data centers and organizations utilizing server racks. 

AnD Cable Products Horizontal Zero U RackOrganizer® offers exceptional savings opportunities for new and old server racks. 

Horizontal Zero U RackOrganizer® with list of benefits

AnD’s Zero U RackOrganizers® are the better alternatives to conventional 1U or 2U cable organizers. Unlike traditional cable managers that occupy their own U space, AnD’s Zero U RackOrganizers® are intelligently designed to mount within the same U space as the active device. As a result, they do not require any additional rack space and will recover 25-30% of rack space currently occupied by conventional cable managers.

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The Future of Server Rack Technology

The future of server rack technology holds great promise, with continuous advancements shaping the landscape of data centers and IT infrastructure. The evolution from custom-built enclosures to standardized, organized, and efficient server racks has revolutionized how we manage and deploy electronic equipment.

As technology progresses, server racks will adapt to meet the ever-changing demands of the digital age. Scalability, energy efficiency, and enhanced cooling solutions will drive future designs, allowing for seamless growth and adaptability. We hope this whitepaper has provided you with all the information you need about what a server rack is, its types, standard dimensions and features, and its history. If you’re a data center manager, an IT entrepreneur, or a tech startup CEO, you should learn more about proper server rack management.

About the Author

Louis Chompff - Founder, AnD Cable Products, Rack and Cable ManagementLouis Chompff, Founder & Managing Director, AnD Cable Products
Louis established AnD Cable Products – Intelligently Designed Cable Management in 1989. Prior to this he enjoyed a 20+ year career with a leading global telecommunications company in a variety of senior data management positions. Louis is an enthusiastic inventor who designed, patented and brought to market his innovative Zero U cable management racks and Unitag cabel labels, both of which have become industry-leading network cable management products. AnD Cable Products only offer products that are intelligently designed, increase efficiency, are durable and reliable, re-usable, easy to use or reduce equipment costs. He is the principal author of the Cable Management Blog, where you can find network cable management ideas, server rack cabling techniques and space saving tips, data center trends, latest innovations and more.
Visit https://andcable.com or shop online https://andcable.com/shop/

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