How to correctly run cables on servers in a data center?

I've read about a few key points, e.g. run all ethernet cables on the right side, all power on the left side, but if possible I'd like to know what you guys do from experience? For example, how do you deal with different cable lengths, where do you put the slack, yet keep it orderly? What's important to keep the cables easily accessible for maintenance?

Thanks guys!

From experience we don't use the "cable management arms" because they just get in the way and impede airflow. That's just us though, you'll find lots of arguments for and against and its not a matter of right or wrong, it's matter of "right for you".

Cabling:

• I like the idea that network cabling runs down one side and power the other where possible. Don't let this become a religion if your needs make this impossible, however. Sometimes you have power requirements that make this impossible - whatever else you do, you should maintain separation of power and data cables as much as possible and certainly never bundle them together.
• You need to label all cables, both ends. Have a dymo labeller available at all times and don't be shy about using it to label anything that might be confusing.
• Plan cable runs, and try and use cable of the right length.
• Keep different types of network cabling seperate. Don't mix bundles of different kinds of cables.
• Remember bend radius - don't pull cable tight.
• You will need a lot of cable ties, both velcro and plastic, use the plastic strips to hold cable that you expect to be there for long term access, and use velcro for stuff that might be changed. Remember that you're not just keeping the place tidy with these ties, you're supporting the cable too.
• Don't "pinch" cable too tightly with plastic ties either, remember that you can damage the cable both by pinching it and by cutting the wrong thing later if you've made it just too gosh darn tight to get your cutters around just the plastic tie. And this could really ruin your day if its a power cable - data centres can be dangerous places - no really, I've had electric shocks twice (due to faulty equipment, not me cutting power cables) and trust me, it stops being funny when it starts being you.
• If you have a suspended floor, or overhead cable baskets, use them. They can be great for cable runs between cabinets, certainly much better than the cats cradles through the side panels I've seen. You'd only want stuff that was permanent done this way though and don't forget to label both ends.

Other considerations: Cabling can be more than just network and power cables, and good cabinet layout is more than just cabling.

• Think about where you will site SAN boxes, tape libraries and switches in a cabinet and plan around good access to those. (don't forget to keep tape libraries at a convenient height for changing tapes!)
• Don't forget to leave space for a KVM box plus monitor tray if you need one - and room to run cables for it of course.
• Make use of both sides of the cabinet - switches should go at the back of the cabinet.
• Whatever you do, remember airflow - cool air should come in at the 'front' of the cabinet and leave at the back. Don't install the servers the wrong way round and don't impede airflow.
• Think about how the cabinet will be used - do people need to access it frequently? Will changes be made to hardware on a frequent basis? Plan accordingly.

Most importantly of all

Whatever else you decide to do, decide to document it as a standard and stick to this standard. Being consistent is one of the most important things you can do.

You should definitely keep power and Ethernet separated as much as possible, to prevent inductive loading of the low-voltage Ethernet from the high voltage/current A/C. In building code, low voltage cannot run parallel to high voltage.

We get rid of cable slack by buying 12", 18", and 24" power cables so we can use exactly as much cable as needed. Ditto for the Ethernet side, though usually there's some slack to take up there. So in those cases I loop the cable at the server end and zip-tie them, making sure not to make the bends too tight -- say 3/4" loop where they bend.

For us, the KVM is more problematic, because our KVM supplier stopped making the 2', 3', and 4' cables, so everything is 6'. But, same sort of thing, loop at the server end.

We use the 3M "command adhesive" loops on the sides of the racks to keep the wires tidy off to the side. These work very well, fit in pretty much any cabinet, and are relatively cheap.