Reference Guide

If buffer credit recovery is enabled, Fabric OS supports a BB_SC_N range of 1 to 15; therefore, it is impossible for the
desired_distance value to be more than the number of buffer credits available in the pool as determined by the previous
calculations The distance for buffer credit recovery is well within the range of all possible connections. An estimated distance of
32,768 is considerably higher than the available buffer credits and only lower values of desired_distance are permitted by
Fabric OS.
Configuring buffers for a single port directly
To configure the number of buffers directly, use the -buffers option of the portCfgLongDistance command. Fabric OS uses this value to
calculate the total number of buffers according to the following formula:
Total Buffers = Configured Buffers + QOS_VC_Credits + Non-data_VC_Credits
Seven Virtual Channels (VCs) are required for each QoS port. Each VC requires two buffers. Thus, the total number of QoS buffers
required for a port is 14 (7*2). An additional 6 VCs are required for nondata transmission (for example, control traffic). As a consequence,
for a QoS port, 20 buffers are added. For a non-QoS port, 6 buffers are added.
For example, if the configured number of buffers is 100, then the total number of buffers allocated for a QoS port is 120, as shown in the
following example.
Total_Buffers = 100 + 14 + 6 = 120
If the configured number of buffers is 100, the total number of buffers allocated for a non-QoS port is 106, as shown in the following
example.
Total_Buffers = 100 + 6 = 106
NOTE
You cannot use the -buffers option with the -distance option or the -frameSize option.
switch:admin> portcfglongdistance 2/35 LS 1 -buffers 400
Reserved Buffers = 420
Configuring buffers using frame size
You can configure the number of buffers by using the -frameSize option of the portCfgLongDistance command along with the -distance
option. Fabric OS calculates the number of buffers from the -frameSize option value according to the following formula:
buffers_required = (2048/ framesize ) * data_vc_credits
If you enter the average frame size of 1024, Fabric OS will allocate almost twice as many buffers as for the maximum frame size of
2048.
The -frameSize option value is persistent across reboots and HA failover.
Example
switch:admin> portcfglongdistance 2/35 LS 1 -distance 100 -framesize 1024
Calculating the number of buffers required given the distance, speed, and frame size
If you know the distance, speed, and frame size for a given port, you can use the portBufferCalc command to calculate the number of
buffers required. If you omit the distance, speed, or frame size, the command uses the currently configured values for the port. Given the
buffer requirement and port speed, you can use the same distance and frame size values when using the portCfgLongDistance
command.
To determine the number of buffers required, complete the following steps:
Buffer-to-Buffer Credits and Credit Recovery
Brocade Fabric OS Administration Guide, 8.0.1
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