Sun Microsystems 96257 ISL Failover Is Supported Only in Shuttle Mode, Performance Considerations

FICON Channel Extension Guidelines

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.

B-82	Sun Confidential: Internal Only	96257
	Revision A