Quality of Service
Cisco UCS provides the following methods to implement quality of service:
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System classes that specify the global configuration for certain types of traffic across the entire system
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QoS policies that assign system classes for individual vNICs
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Flow control policies that determine how uplink Ethernet ports handle pause frames
Global QoS changes made to the QoS system class may result in brief data-plane interruptions for all traffic. Some examples of such changes are:
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Changing the MTU size for an enabled class
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Changing packet drop for an enabled class
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Changing the CoS value for an enabled class
Guidelines and Limitations for Quality of Service on Cisco UCS 6600 Series Fabric Interconnect, Cisco UCS Fabric Interconnects 9108 100G, Cisco UCS 6536 Fabric Interconnects, Cisco UCS 6400 Series Fabric Interconnects
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Multicast optimization is not supported.
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For all QoS system classes except for Fibre Channel, the default MTU is 1500 bytes. The MTU for Fiber Channel class is not configurable and is set to 2240 bytes internally. All classes (excluding Fibre Channel) allow for MTU configuration up to a maximum of 9216 bytes.
Note
The maximum MTU for a QoS class on the Fabric Interconnect is 9216 bytes, while the maximum MTU that can be set on a vNIC is 9000 bytes. The vNIC MTU is configured through the adapter policy.
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The MTU size for fibre channel is always 2240 bytes.
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Multicast is not supported on any no-drop QoS class.