HP 1606 FICON Administrator's Guide v6.4.0 (53-1001771-01, June 2010) - Page 73

IU Pacing, Frame pacing delay, Common FICON issues

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IU Pacing 5 • Blade swapping is not supported when swapping to a different model of blade or a different port count. For example, you cannot swap an FC8-32 blade with an FC8-48 port blade. • Blade swapping is not supported on application blades. NOTE This feature is not supported on the FX8-24 DCX Extension blade. For more information on blade swapping, refer to the Fabric OS Administrator's Guide. IU Pacing IU pacing is not, strictly speaking, a flow control mechanism, as flow control is adequately addressed by the FC-PH level buffer-to-buffer crediting function. Rather, IU pacing is a mechanism intended to prevent I/O operations that might introduce very large data transfers from monopolizing access to Fibre Channel facilities by other concurrent I/O operations. IU pacing provides a load-sharing or "fair-access" mechanism for multiple competing channel programs. While this facility ensures more predictable I/O response times on heavily loaded channels, it produces less optimal results for very-long-distance deployments. In these cases, increased link latencies can introduce dormant periods on the channel and its WAN link. Dormant periods occur when delays waiting for anticipated command responses increase to the point where the pacing window prohibits the timely execution of CCWs that might otherwise be executed to ensure optimal performance. The nominal IU pacing window for 1, 2, 4 and 8 Gbit/sec FICON implementations permits no more than 16 IUs to remain uncredited. Pacing credits can be adjusted dynamically from these values by control unit requests for specific protocol sequences; however, the channel is not bound to honor control unit requests for larger IU pacing windows. Frame pacing delay Common FICON issues Symptom Any information you need to verify that FICON has been set up correctly can be found in the Chapter 2, "Administering FICON Fabrics" or Chapter 3, "Configuring FICON CUP". Cascading: No path - Entry Link is ".." Probable cause and recommended action This typically occurs when one or more of the required high integrity features for cascading have not been met. Check the following: • Review each step in "Configuring switched point-to-point FICON" on page 16 and "Configuring Cascaded FICON" on page 20 and validate that all features are configured properly. • Validate with the data center's system programmer that CUP is online for each director or switch in the fabric. FICON Administrator's Guide 61 53-1001771-01

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FICON Administrator’s Guide
61
53-1001771-01
IU Pacing
5
•
Blade swapping is not supported when swapping to a different model of blade or a different
port count. For example, you cannot swap an FC8-32 blade with an FC8-48 port blade.
•
Blade swapping is not supported on application blades.
NOTE
This feature is not supported on the FX8-24 DCX Extension blade.
For more information on blade swapping, refer to the
Fabric OS Administrator’s Guide
.
IU Pacing
IU pacing is not, strictly speaking, a flow control mechanism, as flow control is adequately
addressed by the FC-PH level buffer-to-buffer crediting function. Rather, IU pacing is a mechanism
intended to prevent I/O operations that might introduce very large data transfers from
monopolizing access to Fibre Channel facilities by other concurrent I/O operations.
IU pacing provides a load-sharing or “fair-access” mechanism for multiple competing channel
programs. While this facility ensures more predictable I/O response times on heavily loaded
channels, it produces less optimal results for very-long-distance deployments. In these cases,
increased link latencies can introduce dormant periods on the channel and its WAN link. Dormant
periods occur when delays waiting for anticipated command responses increase to the point where
the pacing window prohibits the timely execution of CCWs that might otherwise be executed to
ensure optimal performance. The nominal IU pacing window for 1, 2, 4 and 8 Gbit/sec FICON
implementations permits no more than 16 IUs to remain uncredited. Pacing credits can be
adjusted dynamically from these values by control unit requests for specific protocol sequences;
however, the channel is not bound to honor control unit requests for larger IU pacing windows.
Frame pacing delay
Common FICON issues
Any information you need to verify that FICON has been set up correctly can be found in the
Chapter
2, “Administering FICON Fabrics”
or
Chapter 3, “Configuring FICON CUP”
.
Symptom
Cascading: No path – Entry Link is “..”
Probable cause and recommended action
This typically occurs when one or more of the required high integrity features for cascading have
not been met. Check the following:
•
Review each step in
“Configuring switched point-to-point FICON”
on page 16 and
“Configuring
Cascaded FICON”
on page 20 and validate that all features are configured properly.
•
Validate with the data center’s system programmer that CUP is online for each director or
switch in the fabric.