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566 Fabric OS Administrator’s Guide

53-1002745-02

Buffer credit recovery

Buffer credit recovery (CR) allows links to recover after buffer credits are lost when the buffer credit

recovery logic is enabled. The buffer credit recovery feature also maintains performance. If a credit

is lost, a recover attempt is initiated. During link reset, the frame and credit loss counters are reset

without performance degradation.

This feature is supported on E_Ports, F_Ports, and EX_Ports. VE_Ports and VEX_Ports do not

support the portCfgFportBuffers or portCfgLongDistance commands.

Buffer credit recovery is enabled automatically across any long-distance connection for which the

E_Port, F_Port, or EX_Port buffer credit recovery mechanism is supported. For 16-Gbps FC devices

and blades (Brocade 6505, 6510, 6520, CR16-4, CR16-8, FC8-32E, FC8-48E, FC16-32, FC16-48),

you can use the portCfgCreditRecovery command to disable or enable buffer credit recovery on a

port.

Buffer credit recovery over an E_Port

To support buffer credit recovery, E_Ports must be connected between devices that support 16

Gbps or between devices that support 8 Gbps.

• Devices that support 16 Gbps:

- Brocade 6505, 6510, 6520

- FC8-32E, FC8-48E,FC16-32, FC16-48

• Devices that support 8 Gbps:

- Brocade 300, 5100, 5300, 5410, 5424, 5450, 5480, VA-40FC

- FC8-16, FC8-32, FC8-48

If a device that supports 16 Gbps is connected to a device that supports only 8 Gbps, buffer credit

recovery is disabled, even if both devices are running 8 Gbps.

The buffer credit recovery feature for E_Ports is enabled for the following flow-control modes:

• Normal (R_RDY)

• Virtual Channel (VC_RDY)

• Extended VC (EXT_VC_RDY)

Buffer credit recovery over an F_Port

Buffer credit recovery for F_Ports is supported for F_Port-to-N_Port links between a Brocade switch

and Access Gateway, between a Brocade switch and an adapter, and between an Access Gateway

and an adapter. For an F_Port on a Brocade switch connected to an Access Gateway, the following

conditions must be met:

• Both devices must run Fabric OS v7.1 or later.

• Fabric OS must support buffer credit recovery at either end of the link.

• If both devices support16 Gbps, the flow-control mode can be either Normal mode (R_RDY) or

VC mode (VC_RDY); otherwise the flow-control mode must be R_RDY.

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