I hope you enjoyed reading part 1, 2 and 3. As explained Cisco UCS is a converged infrastructure. A converged infrastructure uses less cabling and allows you to configure vNIC’s and vHBA’s as an abstraction layer on top of the physical infrastructure. This offers flexibility and has some benefits. It also adds an important requirement, which is QoS (Quality of Services). Without QoS, any type of traffic could saturate all available bandwidth resulting in slow network or storage performance. Which could potentially make your compute platform unstable. It is important that each type of traffic can consume as much bandwidth as possible when needed, but when the network gets congested each type of traffic gets a fare share of bandwidth, shaped by a pre-defined weight (%).
The nice thing is, Cisco UCS fully supports QoS. In fact, it is an absolute requirement which is easy to configure. QoS is not only used for traffic shaping, it is also used to handle certain type of traffic differently. Like storage traffic (especially Fiber Channel traffic) needs to be lossless (without packet drops). And you might want certain type of traffic (like iSCSI traffic) to use a different MTU packet size (e.g. Jumbo Frames with MTU 9000).