Administrators Guide (Supporting Fabric OS v7.3.0) User Manual

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 following hardware:
• Brocade 300
• Brocade 5100
• Brocade 5300
• Brocade 6505
• Brocade 6510
• Brocade 6520
• Brocade M6505
• Brocade 6547
• Brocade VA-40FC
• Brocade FC8-16, FC8-32, FC8-48, and FC8-64 port blades
• Brocade DCX 8510 Backbone family and supported blades
• Brocade FC16-32 and FC16-48 port blades
• Brocade FC8-32E and FC8-48E port blades
• Brocade FX8-24 application blades in the Brocade DCX and DCX-4S Backbones
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 have either Fabric OS v6.3.0 or
Fabric OS v6.4.0 or later installed to guarantee no frame loss.
Lossless DLS must be implemented along the path between the target and the 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 a fabric topology 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 must 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. The following events cause a rebalance:
• Adding an E_Port
• Adding a slave E_Port
• Removing an E_Port (However, frame loss occurs on traffic flows to this port.)
• Removing an F_Port (However, frame loss occurs on traffic flows to this port.)
Lossless DLS does the following whenever paths need to be rebalanced:
1. Pauses ingress traffic by not returning credits. Frames that are already in transit are not dropped.
2. Changes the existing path to a more optimal path.
Lossless Dynamic Load Sharing on ports
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