Administrator Guide

Fabric OS Administrator’s Guide 453
53-1001763-02
Buffer credit recovery
20
NOTE
QoS requires an additional 14 buffer credits per active port so maximum supported distances may
be lower.
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, VA-40FC
• FC8-16, FC8-32, FC8-48
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.
Virtual E_Ports and Virtual EX_Ports do not support long distance. 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.