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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
When you configure port mode to auto or E on a Generation 3 module, one or two of the ports will not
come up for the following configuration:
• Port Mode: auto or E for the first half of the ports, the second half of the ports or for all of the ports
• Rate Mode: dedicated
• Buffer Credits: default value
When you configure port mode to auto or E for all ports in the global buffer pool, you need to reconfigure
buffer credits on one or more of the ports. The total number of buffer credits configured for all the ports
in the global buffer pool should be reduced by 64.
48-Port 8-Gbps Advanced Fibre Channel Module BB_Credit Buffers
Table 4-1 lists the BB_credit buffer allocation for the 48-port 8-Gbps Advanced Fibre Channel switching
module..
The following guidelines apply to BB_credit buffers on 32/48-port Advanced 8-Gbps Fibre Channel
switching modules:
• 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.
• The buffers should not be allocated automatically.
Each port group on the 32/48-port Advanced 8-Gbps Fibre Channel switching module consists of
four/six ports. The ports in shared rate mode in a port group can have a maximum bandwidth
oversubscription of 1.5:1 considering that each port group has 32-Gbps bandwidth. In case of 32 Port
version, each port group of 4 ports has sufficient bandwidth (32 Gbps) to handle the line rate traffic
without any oversubscription.
The following example configurations are supported by the 48-port Advanced 8-Gbps Fibre Channel
switching modules:
• Six ports with shared rate mode and 8-Gbps speed (1.5:1 oversubscription) (default).
• Two port with dedicated rate mode and 8-Gbps speed plus four ports with shared rate mode and
8-Gbps speed (2:1 oversubscription).
Ta b l e 4-1 48-Port 8-Gbps Advanced 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 250 for 48
port
500 for 32
port
32 32
Maximum BB_credit buffers 500 500 32
