Fabric OS Administrator's Guide v7.0.0 (53-1002148-02, June 2011)

78 Fabric OS Administrator’s Guide
53-1002148-02
Lossless Dynamic Load Sharing on ports
4
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 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 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. Events that cause a rebalance include the
following:
• 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.
3. If IOD is enabled, waits for sufficient time for frames already received to be transmitted. This is
needed to maintain IOD.
4. Resumes traffic.
Table 10 shows the effect of frames when you have a specific routing policy turned on with IOD.
Lossless core
Lossless core works with the default configuration of the Brocade DCX 8510-8 and 6510-4
hardware to prevent frame loss during a core blade removal and insertion. This feature is on by
default and cannot be disabled. Lossless core has the following limitations:
• Only supported with IOD disabled, which means Lossless core cannot guarantee in-order
delivery of exchanges
• ICL limitations
• Traffic flow limitations
ICL limitations
If ICL ports are connected during a core blade removal, it is equivalent to removing external E_Ports
which may cause I/O disruption on the ICL ports that have been removed.
TABLE 10 Combinations of routing policy and IOD with Lossless DLS enabled
Policy IOD Rebalance result with Lossless DLS enabled
Port-based Disabled No frame loss, but out-of-order frames may occur.
Port-based Enabled No frame loss and no out-of-order frames. Topology restrictions apply. Intended
for FICON environment.
Exchange-based Disabled No frame loss, but out-of-order frames may occur.
Exchange-based Enabled No frame loss and no out-of-order frames. Topology restrictions apply. Intended
for FICON environment.