There are a few, but typically most are a combination of copper and fiber due to the cost of the electronics components.
We do, for the most part, copper only within the racks (a stack of Cisco 3750's that live in the rack that provide the RJ45's), then the switches connect via LC's to a structured installation of Multimode fiber to a main distribution point using MPO cables. We find that the MPO's are somewhat more expensive, but allow us to build our own fiber when we need to without having to have a contractor come in and bust out the polishing station.
Does anyone know of any data centers that are fiber only?
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