Server racks are designed for one purpose and that is to provide an easy and secure way to house IT servers and their associated networking devices. Most organisations will have at least one server rack and the problem for many today is how to expand their existing installation to take advantage of new server technologies.
Many of the problems we see when auditing server rooms have their route cause in either a poorly planned initial installation and/or one that has grown rapidly. For the latter, the speed at which a new server is switched-on and being used is more important than what the room and rack looks like. This may be an ‘OK’ approach for some organisations, and especially those that do not have client-facing server facilities, but the practice can reduce IT resilience and introduce potential problems.
So what is the best way to organise and manage a server rack and its deployment?
The following general checklist covers the principle topics for planning a server room and rack cabinet installation:
Racks are available in several height, width and depth combinations. The height is measured in ‘U’s where 1=1.75inches or 44.45mm. All rack mount devices have a corresponding U height making it easy to calculate the total ‘U’ height required for a rack or cabinet. Typical Rack sizes range from 2U (for a small data cabinet) to 47U for a datacentre type server rack.
Racks house devices that are 19inches wide. The depth of the rack with side panels and doors may be wider i.e. 600 and 800mm are the most common widths. The depths can vary from 400 to 1200mm. Choosing the right depth is important to ensure what you want to go into the rack fits. That’s not always as straight forward as it sounds as space at the rear of a device must be consider power and networking cable radius bends.
When selecting a rack for your server room or datacentre you need to consider where it will be placed within the room. The rack must be large enough to accommodate all your IT equipment but must also fit the room. There should be enough room around the front, rear, sides and top of a rack for cooling air flow and access for engineers. A rule of thumb is to allow up to 6 standard floor tiles (600×600mm) as a space onto which to place a server rack.
Server racks and cabinets should not be installed underneath or too close to an air conditioner in case of water leakage or drip problems. These problems can occur if an air conditioning system is not properly designed and regularly maintained or there is a sudden change in the ambient environment that the system was not designed to cope with.
Racks should not be placed within already warm areas (or voids) within a server room. Not all server rooms are uniform or rectangular. L-shaped rooms with side workshops and IT preparation areas are commonly seen. There may be other airflow inhibitors within the room including columns, ‘dumped’ packaging from other installations and/or the room servers a dual purpose as a general archiving area for company records.
The air flow around the rack should not be restricted and the overall air quality and humidity should be ‘acceptable’ and/or managed. What does acceptable mean? Well any are in the room will contain dust and particulate matter that will circulate within the room and be drawn into the IT equipment. If you the air quality is not good enough for anyone working within the room, there’s a good chance that it will eventually cause IT server damage or disruption.
There is a clear health & safety benefit to using a server rack to remove IT servers, cables and even UPS systems from the general floor area where they are potential trip hazards. These can be somewhat negated if the rack installation ‘grows’ haphazardly with interconnecting IT cables between racks and little thought given to rack population and layout.
Consideration should also be given to the size and weight of devices to be housed in a server rack. Any devices mounted into a server rack will require manual handling and for tall racks, working at height. Any engineer or individual tasked with populating or managing equipment within server cabinets and racks should have the appropriate health & safety training and equipment including trolleys and raised platforms do the work. There may also be the need for Risk Assessment and Method Statements (RAMS) to cover required tasks.
Small rackmount devices may be mounted directly onto a rack strut using cage nuts and equipment ears. Larger devices will use slide-out rails, sized to match the depth of the rack and suitable for the weights involved. Care must be taken in terms of over-reaching and the centre of balance of the rack. A heavy slide-out UPS tray at the top of a rack can make a rack ‘top-heavy’ with the potential for a ‘topple’. Heavier weights within a rack may require fixed shelves; these can also be useful for IT devices that cannot be easily rack mounted.
Most organisations have an asset list and each device within a server rack will have its own model SKU and serial number. These three pieces of information along with a description, date of installation and service dates can be recorded onto a rack management spreadsheet. Other additional columns recommended include power draw and heat dissipation or efficiency, UPS (uninterruptible power supply) and PDU (power distribution unit) connections. The document is then maintained when equipment is added or removed and/or maintained. The spreadsheet should cover the entire server room installation and each rack or cabinet within it.
Heat can and will build-up within a server rack and using a managed approach allows you identify potential ‘hot-spots’ that can be checked later with a thermal imaging camera or managed with rack-level environment temperature monitoring. Knowing the power load and heat dissipation helps to accurately size the room air conditioner and manage air flow within the rack. Fan trays and top covers can be used to improve overall cooling and ventilation.
In terms of layout, rack density should be considered. The more ‘free-space’ within a server rack, the greater the room for air flow. Vertical space can be left between servers and IT devices to help cooling. Heat sensitive devices, including UPS batteries can be placed towards the bottom of a server rack, hot air rises. Heavier devices are also best placed towards the bottom of a rack.
Hardware should ideally be logically grouped for ease of management and access to sockets, outlets and ports, whether for power or networking. Ideally within the middle to higher level area of the rack.
A well planned and executed server rack layout is a work of art. Good cable layout makes use of appropriate cable management and labelling so that it is easy to identify both power and network cables. Cable should be marked at both ends for ease of identification and not in the middle. Provision should be made within the layout and cable management system for future work whether its additions or removals. There is nothing worse than trying to trace a cable end and determine the correct device to unplug on a live network.
A solid approach to cable management also helps when there are problems to solve within a server rack. It becomes easier to trace power cords and which PDU is powered which device, or which IT cable is connected to which router or KVM switch port. Ease of access is as important as comfortable access. If there is a KVM switch you need this be at the right height for the person to use it.
Whilst not a great deal of thought may be given to the cabling requirements for a single rack installation, as soon as there are two or more racks the complexity of installation increases. Thought should be given as to the use of patch panels which allow for the use of larger switches and higher port utilisation. Whilst these can add extra cost and take up space within a rack, patch panels do help to simplify rack cable management and especially when there is more than one rack.
A downside is the need to cable between racks and to solve this it may easier to install an ethernet switch in each rack. The use of individual switches reduces cabling between racks and the space requirements within them. Potentially the use of rack level switches can reduce the number of single points of failure as well.
Each device within a server rack will require electrical power and will typically be connected to a PDU. The PDU will either be horizontal (smaller racks) or vertically (larger racks) mounted. The PDU may be remotely monitored over the IP-network and provide options for PDU level or outlet level kWh energy metering and remote-booting.
Each PDU should be supplied from an uninterruptible power supply. UPS may be installed within each server rack (decentralised power protection) or as a centralised power protection plan at the room-level. For the latter a larger UPS is installed to support the sub-distribution board in the room and the critical power circuits including power to the racks as well as cooling, lighting and any other critical infrastructure circuits.
The important point here is to have a robust electrical power protection plan to support the rack deployment both on day-one and to meet future expansion.
Racks are typically placed within the centre of a room. If there is a raised access floor arrangement, this can be used to provide both power and networking cabling to each rack. There should however be clear separation between the cables and uses of shielded cabling.
The alternative is to use overhead cable trays again with separation for power and IT cabling and top-down entry points into the server cabinets. If there is a suspended ceiling, the void is sometimes used for this purpose. It is not ideal however, and any ceiling tile must be appropriately sealed to ensure there is no degradation of the cooling and/or fire suppression system design.
The power demand within server racks continues to rise. 3-5kW is the average with more high-power computing densities pushing up to 10-15kW. This represents a large amount of heat that can lead to a fire hazard if there is a cooling system failure. The larger the power demand of each rack, and the greater the number of racks, the more thought needs to be given to room or rack level fire suppression and environment monitoring. There are several types of room-level fire suppression system and, in-rack fire suppression system trays. Each activates using a ‘double-knock’ approach to provide safe detection and operation.
It is always worth checking with your insurance company as to whether a fires suppression system is required.
More information on rack power densities: https://datacenterfrontier.com/report-data-center-rack-density-is-rising-and-heading-higher/
Within a rising power density, the potential for heat rise and hot spots within a server rack increases. Whilst the room ambient may be stable and well managed to 18-25˚C, internal rack temperatures can rise to 30˚C or more in areas. This localised heat build-up can lead to high rates of equipment malfunction or failure.
It is possible to monitor temperature within a server rack in several ways. Some intelligent PDUs can be installed with additional temperature sensors. The alternative is to install a rack-level or room-level environment monitoring system to which several digital and analogue inputs and digital output devices can be connected.
Room level monitoring provides a greater scope to monitor a wider number of factors including temperature, humidity, water leakage and smoke, as well as motion detection and even server rack access control.
Rack level access control can provide a degree of additional security to an installation and prevent unauthorised access. As a minimum a server room should fall under the building access control system. Each rack cabinet level can also be managed by an access control system if a suitable lock and handle is installed.
These can be wirelessly controlled cabled to the access control system and allow/deny access via a card or mobile token or remote authorisation via the IP network. Additional room security considerations can include CCTV and motion detection cameras.
Additional consideration may be required for industrial or marine type installations. Industrial sites may require dust filters and a higher IP-rating. On-board marine type server racks may require a swing-out frame. It should also be noted that custom metalwork and paint finishes can also be provided by most rack manufacturers and their partners for bespoke projects.
Whether you have a new server room or are expanding an existing datacentre, it is always good practice to go back to first principles when planning a rack installation. Rack power densities are increasing, and IoT, Edge and 5G advancements could lead to a higher use of on-premise server racks and cabinets in the future. It is therefore important to ensure your rack deployment and the equipment housed in the cabinets is documented, labelled and planned. Sound practices like this will ensure that it easier to manage rackmount devices in the future and plan for equipment additions and upgrades.
Data centres and server rooms should be designed around the workload they have to support both from day-one and in the future. This is not always the case and many server room operations evolve from their initial concept, driven by changes in demands, workloads and technology. This can lead to inefficiencies and less than optimum design in terms of critical systems and resilience.