Brocade Fabric OS Administrator's Guide Supporting Fabric OS v6.3.0 (53-1001336-02, November 2009)

66 Fabric OS Administrator’s Guide
53-1001336-02
Lossless Dynamic Load Sharing on ports
4
NOTE
Some devices do not tolerate out-of-order exchanges; in such cases, use the port-based routing
policy.
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.
By default, out-of-order frame-based delivery is allowed to minimize the number of frames dropped.
Enabling in-order delivery (IOD) guarantees that frames are either delivered in order or dropped.
You should only force in-order frame delivery across topology changes if the fabric contains
destination devices that cannot tolerate occasional out-of-order frame delivery.
Forcing in-order frame delivery across topology changes
1. Connect to the switch and log in as admin.
2. Enter the iodSet 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. Confirm the in-order delivery has been set by entering the iodShow command.
Restoring out-of-order frame delivery across topology changes
1. Connect to the switch and log in as admin.
2. Enter the iodReset command.
Lossless Dynamic Load Sharing on ports
Lossless Dynamic Load Sharing (DLS) allows you to rebalance port paths without causing
input/output (I/O) failures in cases where the end devices require In-Order Delivery (IOD) of frames.
You can use this feature with the Brocade 5100 and 5300 switches, and the Brocade DCX and
DCX-4S enterprise-class platforms.
You can use 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 delay caused by establishing a new path when a topology change occurs.
Configuring lossless dynamic load sharing on ports
You configure load sharing on ports by using the iodSet command to specify that no frames are
dropped while rebalancing or rerouting traffic.