ISFC logical link configuration with two non-shared FICON channels and "crossed" FCTC connections
Figure 1 shows an ISFC logical link configuration with two non-shared FICON channels and "crossed" FCTC connections.
Figure 2 shows how the relocation and the quiesce times scale in this case when the amount of FCTC connections configured for the ISFC logical link is varied. Recall that “non-shared” implies that each FICON channel is exclusively used by either LPAR. For the configuration shown, the FICON channel with CHPID 3D is exclusively used by LPAR2, and the FICON channel with CHPID 3E is used exclusively by LPAR1.
Observation
In comparison to the configuration using two shared FICON channels and "crossed" FCTC connections (compare Figure 2 with Figure 2), the relocation and quiesce times are slightly better if only few FCTC connections are used, but slightly inferior if larger amounts of FCTC connections are used. More than four FCTC connections do not cause further improvement, very large number of FCTC connections even cause a slight degradation.
Conclusion
For the interpretation of this result it is important to note that each FICON channel is only used by one LPAR: The sending LPAR (LPAR2) uses one FICON channel for sending the relocation data, the receiving LPAR (LPAR1) uses the other FICON channel for receiving the data. Because each FICON channel is only used in one direction, this comprises a uni-directional usage of the FICON channels.
This is different from the corresponding crossed shared ISFC logical link configuration (see ISFC logical link configuration with two shared FICON channels and "crossed" FCTC connections). With that shared configuration, LPAR2 in fact uses both FICON channels for sending, and LPAR1 simultaneously uses both FICON channels for receiving. Because both FICON channels are simultaneously used for both, sending and receiving data, this comprises a bi-directional usage of the FICON channels.
Comparing the results of the shared and non-shared case with two FICON channels (compare Figure 2 with Figure 2), it can be seen that the relocation and quiesce times using the non-shared configuration are slightly inferior to those using the shared configuration (if an adequate number of FCTC connections is configured). A possible explanation might be the uni-directional versus the bi-directional use of the FICON channels. This is more closely investigated with the inspection of the related ISFC logical link data rates presented in ISFC logical link performance.