Information About Quality of Service
The configurable Cisco NX-OS quality of service (QoS) features allow you to classify the network traffic, prioritize the traffic flow, and provide congestion avoidance.
The default QoS configuration on the device provides lossless service for Fibre Channel and Fibre Channel over Ethernet (FCoE) traffic and best-effort service for Ethernet traffic. QoS can be configured to provide additional classes of service for Ethernet traffic. Cisco NX-OS QoS features are configured using Cisco Modular QoS CLI (MQC).
Standard Ethernet is a best-effort medium which means that it lacks any form of flow control. In the event of congestion or collisions, Ethernet will drop packets. The higher level protocols detect the missing data and retransmit the dropped packets.
Fibre Channel requires a reliable transport system that guarantees the delivery of every packet. To properly support FCoE, Ethernet has been enhanced with a priority flow control (PFC) mechanism to prevent congestion.
The FCoE QoS must be configured either if native FC or FCoE or FC and FCoE are in use. The FCoE QoS must be added even if Ethernet is not configured on the switch.
switch(config)# system qos switch(config-sys-qos)# service-policy type queuing input fcoe-default-in-policy switch(config-sys-qos)# service-policy type queuing output fcoe-default-out-policy switch(config-sys-qos)# service-policy type qos input fcoe-default-in-policy switch(config-sys-qos)# service-policy type network-qos fcoe-default-nq-policy