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Brocade Fabric OS Administrator's Guide Supporting Fabric OS v6.3.0 (53-1001336-02, November 2009)

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Fabric OS Administrator’s Guide 467
53-1001336-02
Buffer credit recovery
20
NOTE
QoS requires an additional 14 buffer credits per active port so maximum supported distances may
be lower.
The 10 Gbps FC10-6 blade has two port groups of three ports each. For extended ISLs, all buffers
available to a group are used to support one port at up to 100 km.
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: 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
• 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.
FC8-48 2461 / 3149 1230 / 1574 615 / 787 307 / 393
FR4-18i 500 250 100 N/A
FS8-18 3208 1604 802 401
FX8-24 2125 1062 531 265
TABLE 91 Configurable distances for Extended Fabrics (Continued)
Maximum distances that can be configured assuming 2112 Byte Frame Size
Switch/blade model 1 Gbps 2 Gbps 4 Gbps 8 Gbps