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One of the most critical is deciding the precise configuration of the internal components. This typically underpins the success of the whole project, especially when IT racks are not installed in a standardised data centre environment.
Meanwhile, choosing which rack to install requires an understanding of its purpose, the routing of cabling for power supply and networks, and the ideal cooling solution. Here are some of the key questions to ask to help ensure the success of any future installation and commissioning of racks.
What will the rack be used for?
The number and type of components will have an impact on the size of the rack. If it will simply be used to house servers, then an IT rack 600mm wide will suffice. However, if it is primarily for network components, the rack should be 800mm wide to accommodate the cabling. But, increasingly, enterprises are combining server and network components within individual IT racks.
As IT takes on an increasingly significant role within organisations, more and more components are packed in to make best possible use of existing infrastructure. This means the largest available racks should be selected – in line with space constraints. An IT rack that is 42 units high, 800mm wide, and 1,200mm deep provides ample room for custom configurations, and allows for future expansion.
What form of climate control is needed?
Will the rack be installed in a room that does not have an integrated cooling system? If so, then a suitable cooling system needs to be considered from the outset. If just a single IT rack is needed then cooling could simply be roof-mounted fans or, if a greater cooling capacity is required, then a compressor cooling unit can be added, either externally or internally, in the form of a DX system – although a higher IP rated rack will be required.
DX systems are becoming more popular as they are relatively easy to install and can be deployed in office environments thanks to the low noise levels of the internal components. Should the rack be deployed in a conventional DC, with either perimeter cooling units or InRow cooling units adjacent to the racks, then perforated doors should be used. Additional benefits can be obtained here by also deploying aisle containment or cocooning, where either the cold or the hot aisle (or in some cases both) is enclosed. The major benefit being lower operating costs and more efficient cooling (better delta T).
There are various options for cooling IT rack interiors depending on their use. For example, inside server enclosures the cool air should flow from front to back, while in network enclosures it should be directed through the parts that need to be cooled.
In both scenarios, it is important to seal around the front 19? section to ensure cool air does not leak into the 'hot zone' at the rack rear and thus lower the delta T across the rack. All open rack units should be closed off with simple 1U snap-off section blanking plates for effective separation. To this end, there is a range of accessories available to enhance cool-air routing, enabling horizontal airflow for side ‘breathing’ switches, and more.
Where do you want your cables?
A detailed plan for interior and exterior cable routing should be in place before a server enclosure is purchased and configured. The power supply, in particular, has to be considered. Many active IT components require a redundant power supply which generally means two rack-mounted vertical power distribution units (PDUs) at the rack rear, left and right for an ‘A’ and ‘B’ supply respectively, making cable management more complex. Moreover, best practice usually recommends power and copper data cables should be kept physically apart to avoid the unlikely possibility of electrical field interference. Special attention must be paid to the minimum bend radius of the fibre-optic cables to prevent signal attenuation.
If the racks are to be placed on a raised floor, then power and network cabling can simply be laid on separate cable trays underneath. You can also mount cables under the ceiling and route them above the top of the racks. In this scenario, the roof plate needs to be configured correctly – openings should be closed off with brush strips creating a tight seal.
Many rack vendors offer a choice of elements for effective cable management, enabling customised component configurations. Both open and closed cable duct systems are available – for horizontal and vertical cabling, and cabling between thermal zones.
Typically, air-tightness and a defined air pressure must be maintained to prevent warm air and cool air from mixing. This important consideration is often built into the design of many rack vendors’ enclosure products.
And external cable management?
Crowded IT racks have little available space to squeeze in new components. One answer is to route cables outside the racks such that cable ducts pass through the side of the rack, routing cabling over the top so that it re-enters the rack from the opposite side. Although this approach can save a great deal of space, it may make identifying individual cables more difficult, and maintenance work more complicated. Wherever easy maintenance is a priority, cables should be routed inside the racks. Pinpointing and replacing a single cable is then far simpler if there is a failure or if a reconfiguration is required.
Innovative products are now becoming available for in rack cable management. One of these is the Network Cable Organiser (NCO), a 482.6 mm (19") cable storage system. It takes up 1U in the network enclosure and contains 24 tested CAT 6, Class E patch cables or fibre-optic cables, each with a length of 1.6 m (sufficient for 23 U).
It has a modular structure and is made up of individual cassettes. The pulley system integrated into the cassettes allows surplus cable lengths to be drawn in automatically which ensures that every cable is available in the perfect length, eliminating the need to order and stock a variety of different cable lengths. The result is permanently well-organised cable, providing a great overview of what is connected where.
It’s also more energy efficient, avoiding airflow blockages that can arise as a result of surplus lengths of the individual cables inside the enclosure, which facilitates more efficient cooling. And the NCO saves on space, because it only requires 1U per switch.
About the author:
Clive Partridge began his career in the merchant navy before becoming a project manager for Siemens in Germany. He joined Rittal Ltd in 1994 as a product manager for electronic and datacomms enclosure products. His experience of water cooled rack products and environmental monitoring led to him taking on the role of Technical Manager for Rittal's IT business, providing expert advice and sales support for colleagues and customers alike.
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