Dell PowerEdge FN I/O Module Command Line Reference Guide 9.10(0.0)

Configure the maximum buffer available for PFC traffic. You can choose to increase or decrease the buffer size that is allocated in the system by default. However, if you modify the PFC buffer size lower than the previously configured size, the system determines whether this reduction in size is valid without disrupting the existing configuration. In such a scenario, disable and re-enable DCB. For example, if you modify the total buffer size as 4000 KB from the previous size of 5000 KB, an error message is displayed that this reduction cannot be performed owing to existing system configuration because of queues that are being currently in process.

The lossless queue limit per port is validated based on the dcb pfc-queues command. PFC queue configuration identifies the maximum number of queues a port can support. Although the queue limit per port is a baseline when dynamic buffering is enabled, the limit per port for queues depends on the availability of the buffer.

Dell(conf)#dcb pfc-total-buffer-size  5000

Dell(conf)#dcb pfc-total-buffer-size  4000 

%ERROR: Total pfc buffer size configured cannot accommodate existing buffer requirement in the system.