How do rack servers work?

Data centres consider rack units, IT cabinets and rack servers a first choice. Different designs and equipment of rack servers provide strong, demand-oriented computing power within a small space in a stable and durable rack enclosure.

Just three years after the introduction of the first web server in 1990, Compaq’s ProLiant series was the first rack server to be developed. Ever since, rack servers have contributed to efficient computing and information processing in data centres. They ensure that secure, cabinet-like enclosures house critical servers and server components in a small space. Their introduction was accompanied by the proliferation of the, now ubiquitous, server rooms.

The term rack server describes the structure of the hardware and software advantages. Rack servers consist of servers and components mounted in standardised 19-inch racks as slide-in units. The rack housing includes mounting slots (rack bays) which mean hardware components can be screwed together securely and stably. The stacking principle ensures easy ventilation of the server system and a higher density of hardware in a smaller space.

The enclosure and mounting grid known as a rack serves as a frame for housing the servers. In the rack, server hardware with server components can be mounted as horizontal or even vertical racks. With their standardised width of 19 inches and various height units, rack servers can be efficiently installed side by side. The installation depth is 60, 80, 100 or 120 centimetres. Other important components are the guides, rails and brackets for cables, sensors, ventilation and cooling units. Depending on safety requirements, they can also include systems for extinguishing gas in an emergency.

Other important components of rack servers are:

• Power supply (PSU)
• CPUs
• Random Access Memory (RAM)
• SSD or HDD
• Network cards or adapters
• RAID controller
• Host bus adapter

Applications for rack servers are manifold. Due to their configurability and the simple scaling and expansion of server components, they’re suitable for small and medium-sized enterprises as well as large data centers. By stacking servers in the rack, resources are consolidated more efficiently and in a space-saving manner.

The main tasks rack servers usually perform include:

• Virtualisation: Rack servers are suitable for virtualization of hardware resources according to the XaaS (Anything-as-a-Service) principle because of their versatile configuration and space-saving installation. This enables IT infrastructures to be effectively reduced while maintaining or improving performance.
• Communication: Rack servers control and manage internal and external communication processes.
• File server: Rack servers often serve as fileservers. They store data and organise access to storage resources in the network.
• Print server: Server racks are also used for dedicated print jobs in a computer network and for routing jobs to printers and plotters.
• Network access server: A rack-mount server can be used to manage access to data, programs or networks in the form of a network access server.
• Storage: Depending on the scope and equipment of rack servers, you can use additional storage resources or consolidate them with other components.

Other areas of application include:

• Proxy server
• DNS server
• Streaming server
• Gaming server
• Mail server

Rack servers differ in their features and dimensions. Racks with the 19-inch standardisation are used most frequently and are usually divided into 2-post racks and 4-post racks. Depending on the width, several server components can be mounted horizontally or vertically in the racks. Vertical height units (rack units) are another important distinction. These have the standardised dimension of 1.75 inches (4.445 centimetres). By default, racks comprise 42 height units.

Since not all slots are equipped from the start, blind panels are also used, i.e. placeholders that provide a better appearance, for example. Basically, the choice of rack server and components depends on the individual performance and space requirements, because this also determines the required height and installation depth

Trends toward more powerful, efficient data centres and growing demand for computing power and performance are driving server hardware to become ever more compact and smaller. Although rack servers are among the most widely used server technologies, rack alternatives such as blade servers and cartridge servers are catching on. These offer more mobility, save space and power, and enable easy scaling and configuration through modular server components.

Micro servers are increasingly being considered as alternatives. However, classic tower servers are another option for small companies without server rooms and demands for high computing power.

The first commercial blade server was launched in 2001 and optimized the server technology of rack servers. Blade servers circumvented a major weakness of rack servers – the space problem caused by many server components in fixed rack-mount frames. Blade servers use a modular chassis with key components in the form of multiple, ultra-thin server blades. This means companies benefit from smaller server hardware with the same or greater computing power. Expansion and maintenance are less complicated, as new components are simply slid in or out of the chassis.

However, blade servers are significantly more expensive to purchase, configure and set up. The replacement of components can also be more complex due to a vendor lock-in. Compared to rack servers, blade servers, which are mostly used for dedicated applications, allow for fewer extensions. That’s because the connections for additional hard disks or PCI slots are usually reduced. Therefore, rack servers are still the first choice for many companies due to their price-performance ratio.