The concept of a remote-end-line-card, aka FEX in Cisco's marketing parlance, is a significant (if not a major) hit. It's so successful that this concept will make a re-incarnation very, very soon.
Depending on what you're hardware is, FEX requires a "mother" controller because the FEX is, literally, a dumb switch. The mother controller acts a single management entity. Controllers comes in various forms, the traditional one is the Nexus 5000/5500, Nexus 6000 (if you want to play with alot of 10 Gbps and a few 40 Gbps), and Nexus 7K.
Be aware, that use the Nexus 7K (to manage 2K), as a last resort. Why? It's is cheaper to buy more Nexus 5K/6K vs buying more 7K as you add more 2K.
You'll also see alot of documentations about dual-homing the Nexus 2K up to two Nexus 5K. Please avoid that temptation. Instead, the best "well proven" practice is to dual/multiple-home your uplink to a single Nexus 5K and dual home your servers to two Nexus 2K.
