NOTHING should ever go vertically across the front or rear of a rack. EVERYTHING should go horizontally into the vertical wire management, up or down within that channel, then out next to the device where it needs to be connected. Assuming you’ve got halfway decent vertical wire management that has a finger every 1U and lots of open space for up to 50 cables each, that gives you an incredibly clean and imminently manageable rack, with nothing interfering with accessing, servicing or removing equipment, you never need horizontal wire management which wastes space in your rack, and it’ll scale up or down nicely from the simplest most well managed rack, to the most hectic/dense/frequently ad-hoc altered rack.
With that, 1m is the bare minimum, but you’ve got lots of room in your vertical wire manager and don’t need to worry about the difference of 0.2m of slack for a cable. So 5ft/1.5m is the shortest I ever get, which is a nice length that covers most nearby connections including server wire management arms. While 7ft/2m is also a convenient size that will connect things up to half a rack away.
