HP StorageWorks 8/80 HP StorageWorks Fabric OS 6.2 administrator guide (5697-0 - Page 365

H1 Domain 1 Domain 3 S1 1 9 H2 14 3 13 12 S2 15 87 = Low priority 16 S3 = Medium priority = High priority = E_Ports with QoS enabled Domain 2 Figure 57 QoS with E_Ports enabled Domain 4 You need to enable QoS on the E_Ports on both ISLs between Domain 3 and Domain 4 because either path might be selected to carry the traffic. You do not need to enable QoS on the E_Ports on the ISLs between Domain 1 and Domain 2 and between Domain 2 and Domain 3, because these are not the shortest paths between the hosts and the targets. However, if the ISL between Domain 1 and Domain 3 is broken, the path through Domain 2 would be used. To guarantee traffic priority, you should enable QoS on all possible E_Ports. Alternatively, you could use a TI zone to limit the E_Ports that carry the traffic between a host,target pair and enable QoS only on those E_Ports. If QoS is not enabled on an E_Port, the traffic prioritization stops at that point. For example, in Figure 57 on page 363 if you disabled QoS on E_Ports 3,12 and 3,13 the traffic from H1 and H2 to S3 would be low priority from the hosts to Domain 3, but would switch to the default (medium) priority from Domain 3 to the target S3. Virtual Fabric considerations for traffic prioritization You can prioritize flows between devices in a Logical Fabric. The priority is retained for traffic going across ISLs and through the base fabric XISLs. For example, Figure 58 shows a Logical Fabric that includes H1 and S1. To set the traffic between H1 and S1 to high priority, create a QoS zone in the Logical Fabric with H1 and S1 as members. Then enable QoS on all of the E_Ports shown circled in the figure, including all of the E_Ports in the XISLs (ports 10, 11, 12, 13, 14, 15, 16, and 17). Fabric OS 6.2 administrator guide 363