Dell PowerConnect Brocade 300 Fabric OS Administrator's Guide v7.1.0 - Page 561
Configuring buffers for a single port directly, Configuring buffers using frame size
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Buffer credit management 23 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. So the total number of QoS buffers required for a port is 14 (7*2). An additional six 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, six 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 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 Total Buffers = 100 + 6 = 106 NOTE You cannot use the -buffers option with the -distance option or the -frameSize option. Example 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. Fabric OS Administrator's Guide 561 53-1002745-02
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