HP StorageWorks Advanced Web Tools 7.4.X Administrator Guide (AA-RVHFC-TE, September 2005)

76 Managing Fibre Channel frame routing
Enabling and disabling in-order frame delivery
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 instance, a link goes
down), traffic is rerouted around the failure. When topology changes occur, some frames can be delivered
out of order.
Enabling in-order delivery (IOD) guarantees that frames are either delivered in order or dropped. In this
case, frames are not delivered out-of-order, even during fabric topology changes. This option should be
used with care, because it causes a delay in the establishment of a new path when a topology change
occurs. This option should be used only if there are devices connected to the fabric that do not tolerate
occasional out-of-order delivery of frames.
The default behavior is for the in-order delivery option to be off. This allows out-of-order delivery of frames
during fabric topology changes and enables fast rerouting after a fabric topology change. Use the
following procedure to enable or disable in-order frame delivery:
1. Access the Switch Manager.
2. Click Administration in the navigation bar.
3. Click the Routing tab.
4. Click the IOD/DLS subtab (see Figure 26 on page 75).
5. Click Edit.
6. Select the in-order delivery option:
• Select In Order Delivery to enforce in-order frame delivery during fabric topology changes.
•Clear In Order Delivery to disable the in-order frame delivery.
7. Click OK.
Enabling and disabling dynamic load sharing
Dynamic load sharing (DLS) refers to a dynamic distribution of traffic over available paths. Enabling DLS
allows load sharing when a fabric change occurs.
Routing is generally based on the incoming port and the destination domain. This means that all the traffic
coming in from an E_Port or an Fx_Port (an Fx_Port is either an F_Port or an FL_Port) that is directed to the
same remote domain is routed through the same output E_Port.
To optimize fabric routing, when there are multiple equivalent paths to a remote switch, traffic is shared
among all the paths. Load sharing is usually recomputed when a switch reboots. If DLS is enabled, load
sharing is also recomputed every time a change in the fabric occurs, such as when an E_Port or Fx_Port
goes up or down.
If DLS is turned off, load sharing is performed only at boot time, when an Nx_Port comes up, or when a
new ISL comes up. Optimal load sharing is rarely achieved with this setting.
DLS is enabled by default. DLS and link cost are not directly related. Routes are calculated based on the
link cost. If there are multiple routes to a destination domain and if DLS is enabled, each local device or
E-Port gets one of the routes.
NOTE: Trunking overrides the DLS setting.
Use the following procedure to enable or disable DLS:
1. Access the Switch Manager.
2. Click Administration in the navigation bar.
3. Click the Routing tab.
4. Click the IOD/DLS subtab (see Figure 26 on page 75).
5. Click Edit.