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Cisco MDS 9000 Family NX-OS Interfaces Configuration Guide
OL-29284-01, Release 6.x
Chapter 4 Configuring Interface Buffers
Information About Interface Buffers
24-Port 4-Gbps Fibre Channel Module BB_Credit Buffers
Table 4-6 lists the BB_credit buffer allocation for 24-port 4-Gbps Fibre Channel switching modules.
The following considerations apply to BB_credit buffers on 24-port 4-Gbps Fibre Channel switching
modules:
• BB_credit buffers for ISL connections can be configured from a minimum of 2 buffers to a
maximum of 250 buffers for dedicated rate mode or 16 buffers for shared rate mode.
• BB_credit buffers for Fx port mode connections can be configured. The minimum is 2 buffers and
the maximum of 250 buffers for dedicated rate mode or 16 buffers for shared rate mode.
• Performance buffers are not supported on this module.
Each port group on the 24-port 4-Gbps Fibre Channel switching module consists of six ports. The ports
in shared rate mode have a bandwidth oversubscription of 2:1 by default. However, some configurations
of the shared ports in a port group can have a maximum bandwidth oversubscription of 4:1 (considering
that each port group has 12.8-Gbps bandwidth).
The following example configurations are supported by the 24-port 4-Gbps Fibre Channel switching
modules:
• Six ports with shared rate mode and 4-Gbps speed (2:1 oversubscription) (default)
• Two ports with dedicated rate mode and 4-Gbps speed plus
four ports with shared rate mode and 4-Gbps speed (with 4:1 oversubscription)
• One port with dedicated rate mode and 4-Gbps speed plus
three ports with dedicated rate mode and 2-Gbps speed plus
two ports with shared rate mode and 4-Gbps speed (4:1 oversubscription)
• Six ports with dedicated rate mode and 2-Gbps speed
• Three ports with dedicated rate mode and 4-Gbps speed plus
three ports with shared rate mode and 1-Gbps speed (see Figure 4-8)
Note For detailed configuration steps of this example, see the “Configuration Example for 24-Port 4-Gbps
Module Interfaces” section on page 3-49.
Tab l e 4-6 24-Port 4-Gbps Switching Module BB_Credit Buffer Allocation
BB_Credit Buffer Allocation
BB_Credit Buffers Per Port
Dedicated Rate Mode
4-Gbps Speed
Shared Rate Mode
4-Gbps Speed
ISL1
1. ISL = E port or TE port.
Fx Port Fx Port
Default BB_credit buffers 250 16 16
Maximum BB_credit buffers 250 250 16
Total number of BB_credits buffers per module 6000