Direct attach versus structured cabling in a data centre

Last week, I had the opportunity to visit one of the bigger, and possibly better, data centres in the Netherlands. This award-winning data centre was the perfect place to see the bigger picture and get a better understanding of how different data centre components work together. It was also one of the bigger data centres I’ve been to. On this note, I learned recently that the average data centre size is about 52 square metres. With half a million data centres worldwide, this would result in 26 square kilometres of data centre space in total. And to put this in perspective, this is the same size as the Polynesian island, Tuvalu, which is located in the Pacific Ocean, midway between Hawaii and Australia.

During this data centre visit I had the opportunity to do some hands-on work on the cable and connector infrastructure, as well as some training of the installers. The installation of the cable assemblies and connector sub-systems is a delicate activity, which can easily go wrong if you don’t follow the proper procedures. What also became clear during my visit is how easily the ducts become full or overloaded, and start to become a nightmare when you need to replace any cables. That’s why I am still a big fan of structured cabling solutions. In these systems, we basically use three different ‘building blocks’ - trunk cables, cassettes, and patch cords. The trunk cables connect the different racks, and are applied in the ducts that are often installed on top of the racks. The cassettes are loaded into the panels inside the racks, and in some cases, at the end of the ducts. The patch cords connect the trunk cables and cassettes on a rack level. The main advantage with working like this is the flexibility it provides when making changes in a data centre without entering the ducts. Basically, when changing the patch cords and/or cassettes, you can increase your bandwidth levels, or align the wiremap to your revised equipment situation.

More information on this can be found here.

Of course, the counter argument is cost and the attenuation budget. By using direct attach cable assemblies, in which the cable connects two pieces of equipment directly, you could say that less parts are required, so a lower cost will be involved. This may be right in some cases, but what about your total applied cost in these circumstances? What if you have a failure and have to replace cables, or what if you have to upgrade your cables to match new equipment and advanced bandwidths? I am not able to give you a specific calculation on this, but you get the picture. Finally, you have to be able to manufacture low attenuation types of interconnects up to 24 fibres per interconnect to offer a complete structured cabling solution.

Next time I will be discussing density in a data centre. Hope to ‘meet’ you again!

Willy Rietveld

W.Rietveld@TE.com