The Cisco UCS uses Data Center Ethernet (DCE) to handle all traffic inside a Cisco UCS domain. This industry standard enhancement to Ethernet divides the bandwidth of the Ethernet pipe into eight virtual lanes. Two virtual lanes are reserved for internal system and management traffic, and you can configure QoS for the other six virtual lanes.

System classes determine how the DCE bandwidth in these six virtual lanes is allocated across the entire Cisco UCS domain. Each system class reserves a specific segment of the bandwidth for a specific type of traffic, which provides a level of traffic management, even in an oversubscribed system. For example, you can configure the Fibre Channel Priority system class to determine the percentage of DCE bandwidth allocated to FCoE traffic. Table 12-5 describes the system classes that you can configure.

Table 12-5 UCS System QoS Class

QoS System Classes Configurations

The type of adapter in a server might limit the maximum MTU supported. For example, network MTU above the maximums might cause the packet to drop for some adapters.

Note

Under the network QoS policy, the MTU is used only for buffer carving when no-drop classes are configured. No additional MTU adjustments are required under the network QoS policy to support jumbo MTU.

You need to use the same CoS values on UCS and Nexus 5000 for all the no-drop policies. To ensure that end-to-end priority-based flow control (PFC) works correctly, have the same QoS policy configured on all intermediate switches.

An example of configuring and enabling LAN QoS is as follows:

Step 1. In the Navigation pane, click LAN. Expand LAN > LAN Cloud.

Step 2. Select the QoS System Class node. The packet drop should be unchecked to configure MTU. MTU is not configurable for drop-type QoS system classes and is always set to 9216. MTU is only configurable for no-drop-type QoS system classes.

Step 3. In the Work pane, click the General tab. Update the properties for the system class that you want to configure to meet the traffic management needs of the system.

Step 4. (Optional) To enable the system class, check the Enabled check box for the QoS system that you want to enable. Then click Save Changes (see Figure 12-59).

Note

Some properties might not be configurable for all system classes. The maximum value for MTU is 9216.

Note

The Best Effort or Fibre Channel system classes are enabled by default. You cannot disable these two system classes. All QoS policies that are associated with a disabled system class default to Best Effort or, if the disabled system class is configured with a CoS of 0, to the CoS 0 system class.