HP Fabric OS v7.0.1, Administrator'S Manual

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76 Fabric OS Administrator’s Guide
53-1002446-01
Lossless Dynamic Load Sharing on ports
4
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 DCX 8510-4
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.
If ICL ports are connected during a core blade insertion, it is equivalent to adding external E_Ports
which may cause I/O disruption due to reroutes. Lossless DLS, if enabled, takes effect to prevent
I/O disruption.
Traffic flow limitations
The FA4-18 and FR4-18i AP blades, which are supported on the Brocade DCX and DCX-4S, may
continue to experience frame drops after core blade removal or insertion. The path between an
FC10-6, FA4-18, or FR4-18i blade and an FX8-24 blade, or vice versa, experiences I/O disruption
because the FC10-6, FA4-18, and FR4-18i blades do not support this feature.
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.