Rackstrip

Have you ever tried to install equipment into a rack, but it doesn’t fit properly because other kit has been installed incorrectly? It’s no surprise really, as some technical staff only get to install rackmount equipment occasionally, and so can easily make this mistake. I see this issue all the time.

Well here is a quick guide for non technical staff to to help you get it right in the future.

A lot of racks are supplied these days have fantastic rackstrip idents, with all the marks for the exact positioning of equipment, some have numbers too which is super helpful if you need to pre-wire racks and need to get cables installed to the right place.

But there are still manufacturers who make basic rackstrip without any markings, and this can be a little confusing for non technical or junior staff.

Some rackstrip has M6 threaded holes instead of the more familiar square cutouts for cage nuts. Here you can see it is difficult to see where one U-space ends and where another begins.

So lets look at the U-space in detail to avoid making this an issue

One rack space 1U is defined as being 1.75” high which is 44.45mm, and has hole for mounting at the top, the bottom and in the middle. There are versions of rackstrip without the middle hole, which is very easy to get right, but the vast majority have the 3 mounting holes. When you look closely you will notice that the spacing between the mount holes is not equal.

The diagram shows the middle hole has larger sides than the edge holes. The centre hole is not often used, but is necessary for some types of servers. The edge holes between two U-spaces has to be very small so that equipment can be installed so that it almost touches. So just remember the middle of the U-Space has the larger sides.

Its’s not a huge problem when they are installed incorrectly, as the cage nuts have a lot of movement in them, and most of the bolts will manage to get in, but when you racks are full, you will not be able to mount some equipment as the space will be too narrow, and quite often the installer will have cross threaded the M6 bolts to make them fit. If you are installing equipment in rackstrip with M6 threaded holes, then you will not be able to get the screws in without cross threading them.

The main problem is when someone has installed something incorrectly, and then more equipment is installed correctly, you end up with a mismatch which then causes larger gaps to be formed. Can you spot which cage nuts are incorrectly fitted?

Recently we were install equipment in a London Data Centre, the rack was relatively empty, and filled mostly with blanking panels to keep the airflow correct for the rack. Having installed our equipment at the top of the rack, we started to replace the blanking plates we’d remove to gain more access. It was then we realised that all the blanking panels were incorrectly installed, and we have to move them all to enable them to fill all the empty spaces within the rack. This time they were quick release plastic ones, but if they had been ones held in with cage nuts, it would have been a lot more work to correct.