Dell PowerConnect Brocade 300 Fabric OS Administrator's Guide v7.1.0 - Page 527

21 QoS zones NOTE By default, QoS is enabled on 8-Gbps ports, except for long-distance 8-Gbps ports. QoS is disabled by default on all 4-Gbps ports and long-distance 8-Gbps ports. H1 Domain 1 Domain 3 S1 1 9 H2 14 3 13 12 S2 15 87 = Low priority 16 S3 = Medium priority = High priority FIGURE 69 = E_Ports with QoS enabled Domain 2 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, then 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 on only those E_Ports. If QoS is not enabled on an E_Port, the traffic prioritization stops at that point. For example, in Figure 69 if you disabled QoS on E_Ports "3,12" and "3,13," then 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. QoS over FC routers QoS over FC routers uses QoS traffic prioritization between devices in edge fabrics over an FC router. See Chapter 24, "Using FC-FC Routing to Connect Fabrics," for information about FC routers, phantom switches, and the FC-FC Routing Service. To establish QoS over FC routers, you must do the following: • Define QoS zones in each edge fabric. • Define LSAN zones in each edge fabric. • Enable QoS on the E_Ports in each edge fabric. • Enable QoS on the EX_Ports in the backbone fabric. See "Setting QoS zone-based traffic prioritization over FC routers" on page 532 for detailed instructions. Fabric OS Administrator's Guide 527 53-1002745-02