RACKS AND ENCLOSURES
onto another common gripe, the issue with server power cords in enclosures. The latest generation of servers may be only 1U high for example, but to accommodate the latest RAID, memory options etc, they need to expand backwards. Before the purchase, it is critical to always purchase at least a 1000mm deep enclosure. Sure, your server or UPS may only be 750mm deep, but you must factor in the cabling at the back, or to be more precise the power cordage. Lower profile or right- angled IEC power cords can help, but please think about cool air flow too.
Messy Cabling Often the cabling is a mess at the rear of the server, pushing to the rear door, out of sight, out of mind. I assure you that this will cause issues. Active equipment will normally have vent fans at the front and back. Normally the back will have fans that will ‘exhaust’ the heat generated from the electronics. However, with a mass of copper spaghetti at the rear blocking the air current, often the air will just circulate the inner walls of the cabinet and increase the overall heat within the enclosure. This may only be by a few degrees, but two points need to be thought about here. Firstly an increase in heat will put extra ‘stress’ on the silicon for example, reducing its MTBF, or life. Secondly, many servers, intelligent switches and UPS use thermostatic control during operation. If the mean temperature reaches a threshold that is deemed to be high it may shutdown the server and any other equipment, preventing serious overheating. You may have had it running okay
during the winter months, during the initial install phase. Have you thought about it running in August during heavy work-time load on the stored databases? On the subject of cooling, have you
factored in enough roof-mounted fan tray options for your equipment? Heat as we know causes convection currents, with the hot air rising to the top space of the enclosure. It needs to escape and escape quickly. It sounds pretty obvious but please make sure the roof fans exhaust the hot air out of a raised and vented roof. I’ve seen many an installation whereby the fans have either spun the wrong way or the fan tray has been placed upside down, causing air to be pushed in but not letting the hot air escape, again causing heating and potential particle and dust problems to build up within the enclosure and equipment.
A mesh door is a priority in allowing cool air to be drawn in. 20 NETCOMMS europe Volume III Issue 3 2013
Top Cooling A rule of thumb for top cooling is a minimum of 4 fans, although a 6 fan configuration will give extra fault tolerance in the event of a fan failing during operation. If it’s a mission critical
server site, consider the installation of intelligent cooling fans in the roof space. These are generally IP configured and the RPM can be monitored with a programmed threshold, so a user can be alerted if the RPM falls too low, giving prior warning of a fan failure. One other feature of some intelligent cooling is that if a fan does fail, the remaining working ones will compensate for the loss by increasing their RPM to maintain a similar ‘litre of air per minute’ exhaust value. Most cabinet accessories such as
fans of course will need power, as will the networking hardware. Sure, the server will be graced with clean power from your expensive online UPS. But consider a filtered PDU solution for the cabinet accessories (especially the intelligent fan trays). Ethernet switches of course use routing tables which will suffer from data corruption in the event of erratic power issues. A filtered PDU will help reduce this issue, keeping your network running smother for longer and reducing data packet corruption still further.
Conclusion Finally, although obvious to most, make sure that the enclosure is fitted with at least a front vented door. As mentioned earlier, the front fans on servers will ‘draw-in’ cool air, so a mesh door is a priority in allowing this. Some vendors allow options to be fitted later, so the standard glass front door can be removed and a vented one fitted accordingly. Don’t forget the transportation of a server enclosure after the kit has been installed. It will be heavy, so make sure that before populating the enclosure, it is fitted with both heavy-duty (ball-raced) castors and adjustable height feet, in case the flooring is uneven. This will also provide a stable environment, which is especially important during equipment maintenance in which an insecure enclosure may cause serious health and safety issues for the IT team.
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