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22-21
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
• By default, 512 performance buffers are preallocated and are shared by all the ports. These buffers
are configurable and the buffers are assigned to the port based on the availability of the buffers in
the shared pool.
• There are 2488 extra buffers available as extended BB_credit buffers after allocating all the default
BB_credit buffers for all the ports in ISL mode (5488 - (250 * 12)).
Note Extended BB_credits are allocated across all ports on the switch. That is, they are not allocated
by port group.
Note By default, the ports in the 12-port 4-Gbps switching modules come up in 4-Gbps dedicated rate mode
but can be configured as 1-Gbps and 2-Gbps dedicated rate mode. Shared mode is not supported.
4-Port 10-Gbps Switching Module BB_Credit Buffers
Table 22-15 lists the BB_credit buffer allocation for 4-port 10-Gbps switching modules.
Note The ports in the 4-port 10-Gbps switching module only support 10-Gbps dedicated rate mode. FL port
mode and shared rate mode are not supported.
The following considerations apply to BB_credit buffers on 4-port 10-Gbps switching modules:
• BB_credit buffers for ISL connections can be configured from a minimum of 2 buffers to a
maximum of 750 buffers.
• BB_credit buffers for Fx port mode connections can be configured from a minimum of 2 buffers to
a maximum of 750 buffers.
Table 22-15 4-Port 10-Gbps Switching Module BB_Credit Buffer Allocation
BB_Credit Buffer Allocation Type
BB_Credit Buffers Per Port
Dedicated Rate Mode
10-Gbps Speed
ISL
1
1. ISL = E port or TE port.
F port
2
2. Ports on the 4-port 10-Gbps cannot operate in FL port mode.
Default BB_credit buffers 250 16
Maximum BB_credit buffers 750 16
Maximum BB_credit buffers on one of the ports with
Enterprise license
4095
Total number of BB_credit buffers per module 5488
Default Performance buffers 145 12
Total number of performance buffers per module 512 (shared)
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