Brocade Fabric OS Administrator's Guide - Supporting Fabric OS v7.0.1 (53-1002446-01, March 2012)

Fabric OS Administrator’s Guide 463
53-1002446-01
Buffer credit recovery
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To get an estimated maximum equally distributed distance for n number of ports at a particular
("X") speed, divide the 1-port maximum distance of the switch at X speed by n. For example, for
three ports running at 2 Gbps on a 300 switch, the maximum equally distributed distance is
calculated as 486 / 3 = 164 km.
Buffer credit recovery
Buffer credit recovery does not require configuration. This feature allows links to recover after
R_RDYs are lost when the 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 only supported on E_Ports that are configured for long distance and are connected
between the following switch or blade models:
• Brocade 300, 5100, 5300, 5410, 5424, 5450, 5480, 6505, 6510, VA-40FC
• FC8-16, FC8-32, FC8-32E, FC8-48, FC8-48E, FC16-32, FC16-48
If a long-distance E_Port from one of these supported switches or blades is connected to any other
switch or blade type, the buffer credit recovery feature is disabled.
VE_Ports and VEX_Ports do not support the portCfgFportBuffers or portCfgLongDistance
commands. The buffer credit recovery feature is enabled for the following flow control modes:
Normal, Virtual Channel (VC), and Extended VC modes.
An FC_Port that supports BB_Credit recovery maintains the following BB_Credit recovery values:
• BB_SC_N is the log2 of BB_Credit recovery modules.
• BB_RDY_N counts the number of R_RDY primitives received modulo 2BB_SC_N.
• BB_FRM_N counts the number of frames received modulo 2BB_SC_N.