HP 1606 Fabric OS Administrator's Guide v6.4.0 (53-1001763-01, June 2010) - Page 119

Lossless Dynamic Load Sharing on ports 4 Lossless Dynamic Load Sharing on ports Lossless Dynamic Load Sharing (DLS) allows you to rebalance port paths without causing input/output (I/O) failures. For devices where In-Order Delivery (IOD) of frames is required, you can set IOD separately. You can use this feature with the Brocade300, 5100, 5300, and VA-40FC switches, and the FC8-16/32/64/48 port blades, the FC8-32 and FX8-18 application blades in the Brocade DCX and DCX-4S enterprise-class platforms. On the Brocade 7800 switch and the FX8-24 application blade, Lossless DLS is supported only on FC to FC port flows. ATTENTION When you implement Lossless DLS, the switches in the fabric must all have either Fabric OS v6.3.0 or they must all have Fabric OS v6.4.0 installed to guarantee no frame loss. Lossless DLS must be implemented along the path between the target and initiator. You can use Lossless DLS on ports connecting switches to perform the following functions: • Eliminate dropped frames and I/O failures by rebalancing the paths going over the ISLs whenever there is a fabric event that might result in suboptimal utilization of the ISLs. • Eliminate the frame delay caused by establishing a new path when a topology change occurs. Lossless mode means no frame loss during a rebalance and only takes effect if DLS is enabled. Lossless DLS can be enabled on fabric topology in order to have zero frame drops during rebalance operations. If the end device also requires the order of frames to be maintained during the rebalance operation then IOD needs to be enabled. However this combination of Lossless DLS and IOD is supported only in specific topologies, such as in a FICON environment. You can disable or enable IOD when Lossless DLS is enabled. You can also choose between exchange- or port-based policies with Lossless DLS. Events that cause a rebalance include the following: • Adding an E-port. • Adding a slave E-port. • Removing an E-port, however frame loss will occur on traffic flows to this port. • Removing an F-port, however frame loss will occur on traffic flows to this port. Lossless DLS does the following whenever paths need to be rebalanced: • Pauses ingress traffic by not returning credits. Frames that are already in transit are not dropped. • Change the existing path to a more optimal path. If IOD is enabled • Wait for sufficient time for frames already received to be transmitted. This is needed to maintain IOD. • Resume traffic. Table 9 shows the effect of frames when you have a specific routing policy turned on with IOD. TABLE 9 Policy Combinations of routing policy and IOD with Lossless DLS enabled IOD Rebalance result with Lossless DLS enabled Port-based Port-based Disabled Enabled No frame loss, but out of order frames may occur. No frame loss and no out of order frames. Topology restrictions apply. Intended for FICON environment. Fabric OS Administrator's Guide 79 53-1001763-01