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20-26
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-17256-03, Cisco MDS NX-OS Release 4.x
Chapter 20 Configuring Interfaces
Buffer Credits
For 16-port switching modules and full rate ports, the default value is 16 for Fx mode and 255 for E or
TE modes. The maximum value is 255 in all modes. This value can be changed as required.
For 32-port switching modules and host-optimized ports, the default value is 12 for Fx, E, and TE modes.
These values cannot be changed.
For Generation 2 and Generation 3 switching modules, see the “Buffer Pools” section on page 22-10.
Note In the Cisco MDS 9100 Series, the groups of ports on the left outlined in white are full line rate. The
other ports are host-optimized. Each group of 4 host-optimized ports have the same features as for the
32-port switching module.
Configuring Buffer-to-Buffer Credits
To configure BB_credits for a Fibre Channel interface using Fabric Manager, follow these steps:
Step 1 Expand Switches > Interfaces and then select FC Physical. You see the interface configuration in the
Information pane.
Step 2 Click the Bb Credit tab.
You see the buffer credits.
Step 3 Set any of the buffer-to-buffer credits for an interface.
Step 4 Click Apply Changes.
This example shows the output of the do show int fc1/1 command:
intfc1/1 is up
...
16 receive B2B credit remaining
3 transmit B2B credit remaining
About Performance Buffers
Note Performance buffers are not supported on the Cisco MDS 9124 Fabric Switch, the Cisco Fabric Switch
for HP c-Class BladeSystem, and the Cisco Fabric Switch for IBM BladeCenter.
Regardless of the configured receive BB_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 Family, you can specify
the amount of performance buffers allocated in addition to the configured receive BB_credit value.
The default performance buffer value is 0. If you set the performance buffer value to 0, the built-in
algorithm is used. If you do not specify the performance buffer value, 0 is automatically used.
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