> # 24-Port 8-Gbps Fibre Channel Module BB_Credit Buffers

> Table 14-3 lists the BB_credit buffer allocation for the 24-port 8-Gbps Fibre Channel switching module.

> Table 14-3 24-Port 8-Gbps Switching Module BB_Credit Buffer Allocation
> BB_Credit Buffer Allocation | BB_Credit Buffers Per Port
> --- | ---
> Dedicated Rate Mode 8-Gbps Speed | Shared Rate Mode 8-Gbps Speed
> ISL | Fx Port | Fx Port
> Default BB_credit buffers | 500 | 32 | 32
> Maximum BB_credit buffers | 5001 | 5001 | 32
> Total Number of BB_Credit Buffers per Module
> Ports 1 through 12 | 6000
> Ports 13 through 24 | 6000

> 1When connected to Generation 1 modules, reduce the maximum BB_credit allocation to 250.

> The following guidelines apply to BB_credit buffers on 24-port 8-Gbps Fibre Channel switching modules:

> - BB_credit buffers allocated for ports 1 through 12 and 13 through 24 can be a maximum of 6000 each so that the load is distributed.
> - BB_credit buffers for ISL connections can be configured from a minimum of 2 buffers to a maximum of 500 buffers for dedicated rate mode.
> - BB_credit buffers for Fx port mode connections can be configured. The minimum is 2 buffers and the maximum of 500 buffers for dedicated rate mode or 32 buffers for shared rate mode.
> - Performance buffers are not supported on this module.

> Each port group on the 24-port 8-Gbps Fibre Channel switching module consists of three ports. The ports in shared rate mode in a port group can have a maximum bandwidth oversubscription of 10:1 considering that each port group has 12.8-Gbps bandwidth.

> The following example configurations are supported by the 24-port 8-Gbps Fibre Channel switching modules:

> - Three ports with shared rate mode and 8-Gbps speed (2:1 oversubscription) (default)
> - One port with dedicated rate mode and 8-Gbps speed plus
>   two ports with shared rate mode and 8-Gbps speed (4:1 oversubscription)
> - One port with dedicated rate mode and 8-Gbps speed plus
>   one port with dedicated rate mode and 4-Gbps speed plus
>   one port with shared rate mode and 8-Gbps speed (10:1 oversubscription)
> - Two ports with dedicated rate mode and 4-Gbps speed plus
>   one port with shared rate mode and 8-Gbps speed (2:1 oversubscription)
> - Three ports with dedicated rate mode and 4-Gbps speed

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