Dell PowerSwitch S4128F-ON OS10 Enterprise Edition User Guide Release 10.4.3.0 - Page 978

• Payload-variable • Cyclic redundancy check-4 bytes • Inter-frame gap-variable The rate adjustment feature is disabled by default. To enable rate adjustment, use the qos-rate-adjust value_of_rate_adjust command. For example: qos-rate-adjust 8 If you have configured WDRR and shaping on a particular queue, the queue can become congested. You should configure the QoS rate adjust value considering the overhead field size to avoid traffic drops on uncongested queues. If you have multiple streams within a queue, you must find the overhead size for the different streams and the QoS rate adjust value should be the highest overhead size from among the various streams within that queue. Consider the example where you have configured WDRR and shaping on a queue that has two different traffic streams, TS1 and TS2, that uses preamble, SFD, and IFG overhead fields: • If the IFG in TS1 uses 16 bytes, QoS rate adjust value should be 24 (preamble + SFD requires 8 bytes and IFG 16 bytes). • If the IFG in TS2 uses 12 bytes, QoS rate adjust value should be 20 (preamble + SFD requires 8 bytes and IFG 12 bytes). In this case, the highest QoS rate adjust value between the two streams is 24 bytes. Hence, you must configure the QoS rate adjust value as 24. NOTE: This feature is not supported on the S4200-ON Series and S5148F-ON platforms. Buffer management OS10 devices distribute the total available buffer resources into two buffer pools at ingress direction and three buffer pools at egress direction of all physical ports. All ports in a system are allocated a certain amount of buffers from corresponding pools based on the configuration state of each prioritygroup or queue. The remaining buffers in the pool are shared across all similarly configured ports. The following buffer pools are available: • Ingress buffer pools: - Lossy pool (default) - Lossless pool (PFC) • Egress buffer pools: - Lossy pool (default) - Lossless pool (PFC) - CPU pool (CPU control traffic) For example, when all ports are allocated as reserved buffers from the lossy (default) pool, the remaining buffers in the lossy pool are shared across all ports, except the CPU port. When you enable priority flow control (PFC) on the ports, all the PFC-enabled queues and priority-groups use the buffers from the lossless pool. OS10 dedicates a separate buffer pool for CPU traffic. All default reserved buffers for the CPU port queues are from the CPU pool. The remaining buffers are shared across all CPU queues. You can modify the buffer settings of CPU queues. You can configure the size of the CPU pool using the control-plane-buffer-size command. OS10 allows configuration of buffers per priority-group and queue for each port. 978 Quality of service