Three families coexist in a modern rack, each in its place:
- DAC (Direct Attach Copper, twinax): copper cable with integrated SFP connectors — unbeatable in price and power draw to link server and switch within the same rack (up to 3–5 m), from 10G to 100G. Its active cousin, AOC, reaches ~30 m.
- RJ45 copper cat. 6A: 10G up to 100 m; still the standard for management (IPMI/iDRAC/iLO) and 1G access. Beyond 10G, copper stops.
- Optical fiber: as soon as you leave the rack, climb in speed (25/100G+) or head to the meet-me room — see OM4 vs OS2.
A healthy rack’s typical layout: DAC inside the rack, OS2 fiber to the outside, one cat. 6A run per server for management — and a fiber patch tray documenting it all.