Marcin's rootprompt blog – /dev/web0

A couple of hints when fitting a 19-inch rack with network and server equipment. I have seen just too many badly fitted racks and messy cabling. Here some of my guidelines.

Placement and environment

• Mind your rack’s placement – the airflow is from front to back, so the front needs to face your cool alley. Blow your cool air at the front, not at the bottom, to maintain optimal air flow and to avoid hot-interior frozen-bottom situations and/or energy waste. The first happens when the equipment sucks up pre-mixed air (not genuinely cold) and the second – when hot air blown out of the equipment is mixed with the cold one from the bottom.
• Any unused space should be filled with dummy plugs at the front to avoid cool air loss. At last – a cheap but not so elegant solution is to use cardboard from your server packaging and screw or zip it tight to rack’s vertical rails. It is not ideal for high pressure systems though.
• If you use blade-alike modular servers, put the chassis at the bottom if your datacenter cooling blows from below. It’s not strictly required if you use side-blowing HVAC.

Cabling

• Plan ahead if you want network cabling in the front or at the back. Front – it’s good to see switch LEDs blinking. Back – switch ports and server ports on the same side, keeping all network cabling at the back.
• Use colors for different network types.
• Fiber optics connecting your FC arrays should definitely stay at the back.
• Organize your distribution – PDUs at the bottom and switches/patch panels at the top. Or other way around, depending on your datacenter setup (or: the direction power lines approach the rack at). Do not mix both for clarity.
• Organize your cabling – networking on one side, power on the other. Use horizontal cable organizers just below your switches and patch panels. Keep cables at the sides with vertical organizers if possible, or get these together with zips to avoid spaghetti effect. If you use a KVM, put its cables at any side too. External rack connections need to be done via rack’s bottom or top vents, not side-to-side.
• Label your cabling – power cords, network, KVM. Just do it during installation phase, otherwise you will most probably never get yourself to do that. Use good labelling supplies – office sticky tape is usually not a good idea. Mark on one end – “server x power supply y” or “server x port y” and on the other – “PDU x outlet y” or “switch x port y“. Upon any changes – always update it. It will save your or your colleagues time, especially during any emergency situation. Yes, it will.
• Remember to leave cable slack if using moving shelves and/or server rails. Use appropriate cable arms if available. Avoid any other loose cabling, zip it.

19-inch Equipment

• If your datacenter does not provide it and you want to install an UPS – put it at the bottom. It’s heavy, and will stabilize your rack. In fact, you do not want to lift it too high to put it anywhere else, right?
• And last but not least – put all your servers facing the front. Do not mix! (yes, I have seen it…)

Optional considerations

• monitoring average temperature in your rack – one sensor in front (at the top to monitor cool air suction), one sensor at the back (behind your hottest gear)
• managed PDUs to control power draw and power-cycle equipment when necessary

Datacenter design is a broad subject, I hope you find these useful. Good luck!