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FICON Channel Extension Guidelines
B-82 Sun Confidential: Internal Only 96257
Revision A
The FICON directors on the supported list provide a port configuration option for link
speed. The VSM port runs in auto-speed mode (currently unconfigurable). The recom-
mendation is to set all FICON director ports attached to extension equipment to a fixed
speed, and to set the attached extension ports to a fixed speed, as follows:
• Set the FICON director port to ‘1Gbps-ONLY’ for attachment to the USD-X channel ex-
tender. Also set the speed of the attached USDX port to ‘1Gbps-ONLY’.
• Set the FICON director port to ‘2Gbps-ONLY’ for attachment to the Edge3000 channel
extender. Also set the speed of the attached Edge3000 port to ‘2Gbps-Only’.
Note: Setting the FICON director port to ‘1Gbps-ONLY’ for the Edge3000 channel ex-
tender attachment is also valid when the WAN link in 1Gbps Ethernet. In this con-
figuration, also set the attached Edge3000 port to ‘1Gbps-ONLY’.
Set Extension Ports to Fixed Speeds When Extending a VTSS-to-VTSS
Channel Link (CLINK) or a VTSS-to-RTD Link
When channel extension is added to a FICON link, the result is two FICON links which are
coupled by the two channel extension chassis through a WAN. The link speed setting on
at least one side of the pair of FICON links must be set to a fixed speed to avoid exposure
to an issue where the link may not initialize once a fibre/SFP cable is attached, or where
the link may not reinitialize after a loss of synchronization during operations.
McData channel extension equipment on the supported list provides a port configuration
option for link speed, which defaults to auto-speed. McData service personnel may per-
form this configuration change to a fixed speed.
The recommendation is to set a least one attached extension port per extended link to a
fixed speed, as follows:
• Set the speed of the attached USD-X chanel extender port to ‘1Gbps-Only’.
• Set the speed of the attached Edge3000 channel extender port to ‘2Gbps-Only’.
Note: Setting the attached Edge3000 port to ‘1Gbps-Only’ is also valid when the WAN
link in 1Gbps Ethernet.
ISL Failover Is Supported Only in Shuttle Mode
McData does not support ISL failover when the extension equipment is configured for
FICON emulation. If extension equipment is configured in FICON shuttle mode, then ISL
failover can be used. Due to distance limitations, shuttle mode is seldom used.
Avoiding Host Protocol Timeouts
Host protocol timeouts may occur due to WAN delays that increase the time for the VTSS
to process multiple outstanding ‘CU busy’ signals. To avoid these timeouts:
• Vary on no more than 16 devices over a channel-extended path to a single VTSS port
• Configure the USD-X or Edge3000 channel extender to support 32 simultaneous emula-
tions by setting the number of emulation control blocks (ECBs) to 32.
Performance Considerations
Consult McData recommendations regarding performance considerations and modes of
operation (i.e., emulation versus shuttle). McData channel extenders emulate write com-
mands, and use shuttle mode (WAN ‘pass-through’) for read commands. When planning
for channel extension, consider the job mix (specifically, the read workload) in combination
with performance requirements, as performance may be significantly affected with the
shuttle mode over certain distances.