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New blog post:  Coping with cable spaghetti, a how-to guide
Jean-Christophe Devalliere's profile photoIan Argent's profile photoWilliam Cinnater's profile photoEric Hsu's profile photo
Cable ties are important.  Also, in a situation like that I would probably buy a box of short cables, 1 or 2 feet.  None of those cables probably needs to be more than 2 feet long.
Agreed, +John Ridley.  I mentioned six-inchers because it looks like those would do for a bunch of the connections in the pair of units at the lower right.
Now we just need a pic of what the utopian version would look like.
+1 for a 12-inch and 6-inch patch cables. They can make what first appear to be insane messes disappear in minutes. 
+Michael Bernstein, that's the stuff I would use as well; lets you measure to length necessary (with a generous extra for future needs, after all, the extra stores neatly.) 
Well layed out plans of mice and men.  I had a similar nightmare which took about six hours to un-fxxk.  The point when I replaced the rats nest of five 50' patch cables with 6" is what drove me to absolute laughter.
As a tip, I find that one of those inline 8P8C female to female adapters is great for snapping on the end of network cables for removing them (from a mess) to keep the retension tabs from being snapped off.  Of course, it's even better if the cable was manufactured with one of those boots which serves the same purpose.

A few questions, if you don't mind...

Removing everything then building it back up means more downtime (I would think) because (individual) things are down as cables are removed, the whole thing is completely down at approx. the midpoint, and it's not completely back online until you're done.  Is there a rationale behind not replacing one cable at a time? It's a different problem of course, but one at a time is the way I'd replace spark plug wires and/or spark plugs so that there is very little chance of getting the wrong firing order.  Likewise, if cables were replaced one at a time, I'd think this would be at least somewhat less error-prone because there will be a cable end hanging there somewhere around each socket, and it's at least possible to test each reconnection individually, instead of getting to the end and wondering "holy crap! It doesn't (completely) work, so where in that whole exercise did I frak up?"

What do you think about custom making at least some of the connections with a spool of cable and connectors (for wire anyway, probably not as practical as optical)?  That way, they're exact length with no or only moderate excess (I always leave a little slack if I can).  The potential tradeoffs of course are reliability, as premanufactured cables are quite usually tested and presumed good, plus it takes (usually nontrivial) time to put the connectors on.
The reason I don't try to replace one cable at a time is that if you do that it's harder to avoid creating another hairball, even if you're using short cables.

Yes, there are setups where a couple of hours' downtime isn't tolerable. For those you have to use a different (and more difficult) technique.

Custom cables are nice if you have the equipment to make them, and the experience to make them reliable, and a cable tester on hand so as you make each one you can check that you're not introducing a hidden wiring fault. In a good many of these situations, alas, you can't even budget for the equipment.
Heh ... an active cable tester was the first thing I got after I got the RJ-45 crimping tool.  Making your own cables without testing them is like daring Murphy and Finagle to have a taffy pulling contest, with you as the taffy.
I had a nightmare rack rewire once at a former employer.  The core of the company network was a single 72-port shared 10BT hub, and half the machines in the company were Macs.  Collision rate would sit at 50% or higher for minutes at a time.  The main patch panel was right above the hub, and the entire damn thing was wired with 20' cables.  Some of them made three complete turns of the cable-management stanchions around the hub before diving into the mess to reach a port.

I ordered a bale of a hundred 1m cables, then one Friday evening I tore out the entire thing and rewired it from scratch.  Then you could actually see the ports and see what was connected to what, but the network was still saturated.  Then later on, I tore out the Asante hub and replaced it with a realistic stack of 10/100 switches.  After that, the network was actually usable.
the problem is that they failed to use proper cable management.  They should have installed at least horizontal cable ducts or lace bars, and preferably added vertical race-ways as well.
+John Smith, you obviously haven't seen racks with neatly installed cable ducts, lace bars, and vertical raceways underneath the rats' nest...
I've seen many many mismanaged racks all over the world.  Not having proper cable management hardware installed exasperates the problem.
That's "exacerbates", although the problem can indeed be quite exasperating.

And having the hardware installed merely increases the cost of the rack without improving the likelihood that people actually manage cables well, IME.
I like "exasperates."  I vote for adding it to the dictionary!
+Jay Maynard If it's not there, they won't have a chance to use it.  Penny pinching on the rack hardware in the beginning is a sure way to  lead to spending more money in the long run.  It's common to walk into a colo and find the lack of planning and being cheap ends up with fiber swung from rack to rack, and the exhaust from the back of one server blowing into the front of another. Tangled messes of power cords, over loaded UPS and air conditioning leads to downtime.

The thing to take away from this is that you should do it right the first time, or get out of the business, because you are just causing problems for everyone who follows after you. 

+Ken Barber  After a series of 16 hour days that start at midnight, my spelling stats to  fail.
Oh, I agree that if it's not installed up front, it won't get used. It's just that I don't have a lot of confidence that it gets used anyway, based on seeing folks just plain ignore it. It's like commenting code: people know they should, but do they?
Yes, and that is where craftsmanship becomes relevant .. something I often see lacking in the field.  Ther's no comparison between the beauty of the old Western Electric cable work, with their meticulous lashed cable to that of today's net rats nests with diagonal patching and bundles of patch cables the size of one's thigh
Sadly all my racks look like this and my response to the boss normally is "then go hire an inside plant guy / rack monkey" :) :)
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