Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 283

Buffer Sizes for Lossless or PFC Packets You can configure up to a maximum of 4 lossless (PFC) queues. By configuring 4 lossless queues, you can configure 4 different priorities and assign a particular priority to each application that your network is used to process. For example, you can assign a higher priority for time-sensitive applications and a lower priority for other services, such as file transfers. You can configure the amount of buffer space to be allocated for each priority and the pause or resume thresholds for the buffer. This method of configuration enables you to effectively manage and administer the behavior of lossless queues. Although the system contains 12 MB of space for shared buffers, a minimum guaranteed buffer is provided to all the internal and external ports in the system for both unicast and multicast traffic. This minimum guaranteed buffer reduces the total available shared buffer to 9.5 MB. This shared buffer can be used for lossy and lossless traffic. The default behavior causes up to a maximum of 6.6 MB to be used for PFC-related traffic. The remaining approximate space of 1 MB can be used by lossy traffic. You can allocate all the remaining 1 MB to lossless PFC queues. If you allocate in such a way, the performance of lossy traffic is reduced and degraded. Although you can allocate a maximum buffer size, it is used only if a PFC priority is configured and applied on the interface. The number of lossless queues supported on the system is dependent on the availability of total buffers for PFC. The default configuration in the system guarantees a minimum of 52 KB per queue if all the 128 queues are congested. However, modifying the buffer allocation per queue impacts this default behavior. By default the total available buffer for PFC is 6.6 MB and when you configure dynamic ingress buffering, a minimum of least 52 KB per queue is used when all ports are congested. By default, the system enables a maximum of 1 lossless queue on the switch. This default behavior is impacted if you modify the total buffer available for PFC or assign static buffer configurations to the individual PFC queues. Configuring the Dynamic Buffer Method Priority-based flow control using dynamic buffer spaces is supported on the switch. To configure the dynamic buffer capability, perform the following steps: 1 Enable the DCB application. By default, DCB is enabled and link-level flow control is disabled on all interfaces. CONFIGURATION mode dcb enable 2 Configure the shared PFC buffer size and the total buffer size. A maximum of 4 lossless queues are supported. CONFIGURATION mode dcb pfc-shared-buffer-size 2000 dcb pfc-total-buffer-size 5000 3 Configure the number of PFC queues. CONFIGURATION mode dcb enable pfc-queues pfc-queues The number of ports supported based on lossless queues configured will depend on the buffer. The default number of PFC queues in the system is two. For each priority, you can specify the shared buffer threshold limit, the ingress buffer size, buffer limit for pausing the acceptance of packets, and the buffer offset limit for resuming the acceptance of received packets. 4 Configure the profile name for the DCB buffer threshold Data Center Bridging (DCB) 283