Dell Brocade G620 Brocade 8.0.1 Fabric OS Administratiors Guide - Page 130
Calculating the number of buffers required based on full-size frames
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Buffer-to-Buffer Credits and Credit Recovery Refer to the data in Table 14 on page 135 and Table 17 on page 136 to get the total ports in a switch or blade, the number of user ports in a port group, and the unreserved buffer credits available per port group. The values reflect an estimate, and may differ from the supported values in Table 17 on page 136. Calculating the number of buffers required based on full-size frames Use the following procedure to calculate the number of buffers required for a long-distance connection: 1. Determine the desired distance in kilometers of the switch-to-switch connection. 2. Determine the speed that you will use for the long-distance connection. 3. Use one of the following formulas to calculate the reserved buffers for distance: ∙ If QoS is enabled: (Reserved_Buffer_for_Distance_Y) = (X * LinkSpeed / 2) + 6 + 14 ∙ If QoS is not enabled: (Reserved_Buffer_for_Distance_Y) = (X * LinkSpeed / 2) + 6 The formulas use the following parameters: X = The distance determined in step 1 (in km). LinkSpeed = The speed of the link determined in step 2. 6 = The number of buffer credits reserved for fabric services, multicast, and broadcast traffic. This number is static. 14 = The number of buffer credits reserved for QoS. This number is static. Using 50 km as the desired distance of the switch-to-switch connection and 2 Gbps as the speed of the long-distance connection, insert the numbers into the appropriate formula. The formula should read as follows: (50 km * 2 Gbps / 2) + 6 = 5 6 buffers, which is the number of buffers reserved for distance. The following examples use different speeds, all based on a distance of 50 km. The distances and speeds are variables that can change depending on how your network is set up. ∙ If you have a distance of 50 km at 1 Gbps, then (50 km * 1 Gbps / 2) + 6 = 31 buffers. ∙ If you have a distance of 50 km at 2 Gbps, then (50 km * 2 Gbps / 2) + 6 = 56 buffers. ∙ If you have a distance of 50 km at 4 Gbps, then (50 km * 4 Gbps / 2) + 6 = 106 buffers. ∙ If you have a distance of 50 km at 8 Gbps, then (50 km * 8 Gbps / 2) + 6 = 206 buffers. ∙ If you have a distance of 50 km at 10 Gbps, then (50 km * 10 Gbps / 2) +6 = 256 buffers. ∙ If you have a distance of 50 km at 16 Gbps, then (50 km * 16 Gbps / 2) + 6 = 406 buffers. ∙ If you have a distance of 50 km at 32 Gbps, then (50 km * 32 Gbps / 2) + 6 = 806 buffers. Example Consider the Brocade 300, which has a single 24-port port group and a total of 676 buffer credits for that port group. The formulas use the following parameters: 24 = The number of user ports in a port group retrieved from Table 14 on page 135 8 = The number of reserved credits for each user port 676 = The number of buffer credits available in the port group The maximum remaining number of buffer credits for the port group, after each port reserves its 8 buffer credits, is obtained from the following formula: Brocade Fabric OS Administration Guide, 8.0.1 130 53-1004111-02
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