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22-16
Cisco MDS 9000 Family Fabric Manager Configuration Guide
OL-17256-03, Cisco MDS NX-OS Release 4.x
Chapter 22 Configuring Generation 2 and Generation 3 Switching Modules
Buffer Credit Allocation
4/44-Port 8-Gbps Host-Optimized Fibre Channel Module BB_Credit Buffers
Table 22-10 lists the BB_credit buffer allocation for the 4/44-port 8-Gbps Fibre Channel switching
module.
The following guidelines apply to BB_credit buffers on 4/44-port 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 250 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 12 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 4/44-port 8-Gbps Fibre Channel switching
modules:
• Twelve ports with shared rate mode and 4-Gbps speed (5:1 oversubscription) (default)
• One port with dedicated rate mode and 8-Gbps speed plus
eleven ports with shared rate mode and 4-Gbps speed (10:1 oversubscription)
• One port with dedicated rate mode and 4-Gbps speed plus
three ports with dedicated rate mode and 3-Gbps speed plus
eight ports with shared rate mode and 4-Gbps speed (2:1 oversubscription)
• Twelve ports with dedicated rate mode and 1-Gbps speed
Table 22-10 4/44-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 125 32 32
Maximum BB_credit buffers 250 250 32
Total number of BB_credit buffers per module 6000
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