HP StorageWorks 4/256 HP StorageWorks Fabric OS 5.2.x administrator guide (569 - Page 193
Using Dynamic Load Sharing, To force in-order frame delivery across topology changes
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In a stable fabric, frames are always delivered in order, even when the traffic between switches is shared among multiple paths. However, when topology changes occur in the fabric (for example, if a link goes down), traffic is rerouted around the failure, and some frames could be delivered out of order. Most destination devices tolerate out-of-order delivery, but some do not. Use of out-of-order frame-based delivery can minimize the number of frames dropped, while enabling in-order delivery (IOD) gurantees that frames are either delivered in order or dropped. All HP B-series switches enable IOD by default to ensure frames are delivered in order, as not all HP destination devices can tolerate out-of-order frames. To force in-order frame delivery across topology changes 1. Connect to the switch and log in as admin. 2. At the command line, enter the iodReset command. NOTE: This command can cause a delay in the establishment of a new path when a topology change occurs; use it with care. 3. To confirm the In Order Delivery has been set, issue the iodShow command. To restore out-of-order frame delivery across topology changes 1. Connect to the switch and log in as admin. 2. Enter the iodSet command at the command line. Using Dynamic Load Sharing The exchange-based routing policy depends on the Fabric OS Dynamic Load Sharing feature (DLS) for dynamic routing path selection. When using the exchange-based routing policy, DLS is by default enabled and cannot be disabled. In other words, you cannot enable or disable DLS when the exchange-based routing policy is in effect. When the port-based policy is in force, you can enable DLS to optimize routing. When DLS is enabled, it shares traffic among multiple equivalent paths between switches. DLS recomputes load sharing when a switch boots up or each time an E_Port goes offline and online, or a Fx_Port goes offline. To check and set DLS 1. Connect to the switch and log in as admin. 2. Enter the dlsShow command to view the current DLS setting. One of the following messages appears: • "DLS is set" indicates that dynamic load sharing is turned on. • "DLS is not set" indicates that dynamic load sharing is turned off. • "DLS can not be changed with current routing policy" indicates that you are using the exchange-based routing policy and you cannot enable or disable DLS. 3. Enter the dlsSet command to enable DLS or enter the dlsReset command to disable it. switch:admin> dlsshow DLS is not set switch:admin> dlsset switch:admin> dlsshow DLS is set switch:admin> dlsreset switch:admin> dlsshow DLS is not set Fabric OS 5.2.x administrator guide 193
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