Dell Force10 S4820T S4820T Configuration Guide - Page 304

www.dell.com | support.dell.com FTOS Behavior: Traffic in priority groups is assigned to strict-queue or WERR scheduling in an ETS output policy and is managed using the ETS bandwidth-assignment algorithm. FTOS de-queues all frames of strict-priority traffic before servicing any other queues. A queue with strict-priority traffic can starve other queues in the same port. ETS-assigned bandwidth allocation and scheduling apply only to data queues, not to control queues. FTOS supports hierarchical scheduling on an interface. FTOS control traffic is redirected to control queues as higher priority traffic with strict priority scheduling. After control queues drain out, the remaining data traffic is scheduled to queues according to the bandwidth and scheduler configuration in the ETS output policy. The available bandwidth calculated by the ETS algorithm is equal to the link bandwidth after scheduling non-ETS higher-priority traffic. The configuration of bandwidth allocation and strict-queue scheduling is not supported at the same time for a priority group. If both are configured, the configured bandwidth allocation is ignored for priority-group traffic when you apply the output policy on an interface (refer to Applying an ETS Output Policy for a Priority Group to an Interface). Bandwidth assignment in a dot.1p priority-queue: By default, equal bandwidth is assigned to each port queue and each dot1p priority in a priority group. Use the bandwidth-percentage command to configure bandwidth amounts in associated dot1p queues. When specified bandwidth is assigned to some port queues and not to others, the remaining bandwidth (100% minus assigned bandwidth amount) is equally distributed to unassigned non-strict priority queues in the priority group. The sum of the allocated bandwidth to all queues in a priority group should be 100% of the bandwidth on the link. Bandwidth assignment in a priority group: By default, equal bandwidth is assigned to each priority group in the ETS output policy applied to an egress port if you did not configure bandwidth allocation. The sum of configured bandwidth allocation to dot1p priority traffic in all ETS priority groups must be 100%. You must allocate at least 1% of the total bandwidth to each priority group and queue. If you assign bandwidth to some priority groups but not to others, the remaining bandwidth (100% minus assigned bandwidth amount) is equally distributed to non-strict-priority groups which have no configured scheduler. Scheduling of priority traffic: dot1p priority traffic on the switch is scheduled to the current queue mapping. dot1p priorities within the same queue should have the same traffic properties and scheduling method. ETS output-policy error: If an error occurs in an ETS output-policy configuration, the configuration is ignored and the scheduler and bandwidth allocation settings are reset to the ETS default values (all priorities are in the same ETS priority group and bandwidth is allocated equally to each priority). If an error occurs when a port receives a peer's ETS configuration, the port's configuration is reset to the previously configured ETS output policy. If no ETS output policy was previously applied, the port is reset to the default ETS parameters. 304 | Data Center Bridging (DCB)