HP Fabric OS 7.1.0, Administrator'S Manual

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Fabric OS Administrator’s Guide 561
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Buffer credit management
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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.