Information About Interface Buffers; Buffer-To-Buffer Credits; Performance Buffers; Buffer Pools - Cisco MDS 9000 Series Configuration Manual

Configuring Interface Buffers

Information About Interface Buffers

Fibre Channel interfaces use buffer credits to ensure all packets are delivered to their destination.

Buffer-to-Buffer Credits

Buffer-to-buffer credits (BB_credits) are a flow-control mechanism to ensure that Fibre Channel switches do
not run out of buffers, so that switches do not drop frames.
The receive buffer-to-buffer credit (fcrxbbcredit) value may be configured for each Fibre Channel interface.
In most cases, you do not need to modify the default configuration.

Performance Buffers

Regardless of the configured receive buffer-to-buffer credit value, additional buffers, called performance
buffers, improve switch port performance. Instead of relying on the built-in switch algorithm, you can manually
configure the performance buffer value for specific applications (for example, forwarding frames over FCIP
interfaces).
For each physical Fibre Channel interface in any switch in the Cisco MDS 9000 Series, you can specify the
amount of performance buffers allocated in addition to the configured receive buffer-to-buffer credit value.
The default performance buffer value is 0. If you use the default option, the built-in algorithm is used. If you
do not specify this command, the default option is automatically used.

Buffer Pools

In the architecture of 4-Gbps, 8-Gbps, 16-Gbps, and 32-Gbps modules, receive buffers shared by a set of ports
are called buffer groups. The receive buffer groups are organized into global and local buffer pools.
The receive buffers allocated from the global buffer pool to be shared by a port group are called a global
receive buffer pool. Global receive buffer pools include the following buffer groups:
• Reserved internal buffers
• Allocated buffer-to-buffer credit buffers for each Fibre Channel interface (user configured or assigned
• Common unallocated buffer pool for buffer-to-buffer credits, if any, to be used for additional

Buffer-to-Buffer Credit Buffers for Switching Modules

This section describes how buffer credits are allocated to Cisco MDS 9000 Series Multilayer switches.
by default)
buffer-to-buffer credits as needed
Cisco MDS 9000 Series Interfaces Configuration Guide, Release 8.x
Information About Interface Buffers
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