HP StorageWorks 8/80 HP StorageWorks Fabric OS 6.2 administrator guide (5697-0 - Page 430
Displaying the remaining buffers in a port group
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1. Determine the desired distance in kilometers between the switch-to-switch connection. This example uses 50 km. 2. Determine the speed that you will use for the long-distance connection. This example uses 2 Gb/s. 3. Use the following formula to calculate the reserved buffers for distance: (Reserved Buffer for Distance Y) = (X * LinkSpeed / 2) + 6 Where: X = the distance determined in step 1 (in kilometers). 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 is a static number. Based on the answers provided in steps 1 and 2, insert the numbers into the formula. The formula should read as follows: (50 km * 2 Gb/s / 2) + 6 = 56 buffers, which is the number of buffers reserved for distance Below are additional examples using different speeds all based on a distance of 50 km. The distances and speeds are variables that can change based on how your network is set up. • If you have a distance of 50 km at 1 Gb/s, then,(50 km * 1 Gb/s / 2) + 6 = 31 buffers • If you have a distance of 50 km at 2 Gb/s, then (50 km * 2 Gb/s / 2) + 6 = 56 buffers • If you have a distance of 50 km at 4Gb/s, then,(50 km * 4 Gb/s/ 2) + 6 = 106 buffers • If you have a distance of 50 km at 8 Gb/s, then (50 km * 8 Gb/s/ 2) + 6 = 206 buffers Example: Consider the HP StorageWorks 8/8 and 8/24 SAN Switches, which have a single 24-port port group and a total of 676 buffer credits for that port group The maximum remaining number of buffer credits for the port group, after each port reserves its eight buffer credits is: 676 - (24 * 8) = 484 unreserved buffer credits Where: 24 = the number of user ports in a port group retrieved from Table 82 on page 427. 8 = the number of reserved credits for each user port. 676 = the number of buffer credits available in the port group. If you allocate the entire 484 + 8 (8 for the reserved buffers already allocated to that user port) = 492 buffers to a single port, you can calculate the maximum single port extended distance supported: [Maximum Distance X in km] = (BufferCredits + 6) * 2 / LinkSpeed 498 km = (492 + 6 buffers for Fabric Services) * 2 / 2 Gb/s How many 50 km ports can you configure? If you have a distance of 50 km at 8 Gb/s, 484 / (206 - 8) = 2 ports The numbers used are: 484, which equals the total number of unreserved buffer credits, 206, which equals buffer credits needed for 50 km @ 8 Gb/s (calculated previously), and 8, which equals number of reserved buffer credits already allocated to that port. The floor of the resulting number is taken because fractions of a port are not allowed. If you have a distance of 50 km at 1 Gb/s, 484 / (31 - 8) = 21 ports Displaying the remaining buffers in a port group Enter the portBufferShow command to display all of the long-distance buffer information for all the port groups of the switch. Use the following syntax: portbuffershow [[slotnumber/]portnumber] slotnumber For bladed systems only, specifies the slot number of the port group to display, followed by a slash (/). portnumber Specifies the number of a port associated with the port group, relative to its slot for bladed systems. Use the switchShow command to display a list of valid ports. 426 Administering extended fabrics