Thursday, March 3, 2011

Home Made Cable Spaghetti

Rack of equipment entangled in a messy mass of cables

I wrote some thoughts for a colleague about home installation of a rack for computer equipment. Much of it is generally applicable for anyone considering such a thing, presented here for your edification and bemusement.

  • buy extra rack screws, maybe 20. The cheap ones strip easily, and nothing sucks harder than getting a new system in only to discover you've run out of rack screws.
  • Get an electric screwdriver if you don't already have one.
Physical Installation
  • Bolt the rack to the floor and the ceiling. Otherwise an earthquake which doesn't otherwise damage the house can rip the rack out of the floor. The rack itself will be shorter than ceiling height, you get an extended brace to bolt to the ceiling. You want to bolt it to joists, not just drywall.
  • There are also racks made to bolt to the wall rather than free standing floor to ceiling. These tend not to be as deep front to back, so it impacts the gear you can put in it. Also they can be an airflow problem if the gear vents front to back.
  • Perhaps obviously, when filling the rack start from the bottom and put the heaviest gear at the very bottom. A top-heavy rack is a disaster.
  • The industry never settled on whether airflow is front to back or side-to-side. You'll find equipment with both layouts. With one rack it doesn't particularly matter, and you can mix them. With multiple racks it matters a lot.
  • The industry also never settled on whether rack ears go at the very front of the equipment or the midpoint. Front is most common, to accommodate boxes of differing depths. Lots of gear has threaded screwholes at front and midpoint, just be consistent.
  • 19 inch racks are by far the most common, but be aware that 17 inch and 23 inch both exist. They will be well-labelled in catalogs as they are not common. If you buy second hand, bring a tape measure.
Cable Management
  • Spend as much time thinking about cable management as you do about how to rack the machines. Otherwise you end up with a beautiful rack covered in cable spaghetti.
  • Its customary to put the network switch at the top of the rack, because gravity makes cable management easier. However its not essential, and you can put it anywhere you like.
  • There are cable trays with removable fronts made to bolt vertically to the side of the rack or between adjacent racks. HIghly recommended.
  • Label both ends of each cable. Label them in a way which will still make sense in a few years when you replace these machines and have forgotten everything about the construction.
  • Avoid labeling cables according to their destination within the rack. That changes over time, relabeling cables is a pain.