IOCDS configuration for FICON CTCs

Initially three FICON® channels from a FICON Express4 channel card were available.

In a later phase, we could use a second FICON Express4 channel card. In the IOCDS configuration for the CEC, these three FICON channels were assigned CHPIDs 3C, 3D and 3E; these FICON channels were used to configure FICON CTC (FCTC) connections that connect LPAR1 and LPAR2 in various ways.

FCTC connections

For the purposes of this document, the term "FCTC connection" is used to refer to the pair of FCTC devices that are configured to be connected by means of the IOCDS configuration; for details, see System z®, ESCON and FICON Channel-to-Channel Reference. Occasionally, the term "FCTC device" could mean both "FCTC device" and "FCTC connection".

A graphic representation of the IOCDS based FCTC configuration is shown in Figure 1.

Block diagram showing FICON FCTC configuration — Figure 1. FCTC configuration

For each of the two LPARs, sets of FCTC connections were configured in the IOCDS, such that LPAR1 could potentially connect to LPAR2 through every possible FICON channel combination. Each possible FICON channel combination was configured with 16 FCTC devices on each side, resulting in 144 possible FCTC connections. The recommended convention of assigning the same device number for both FCTC devices of an FCTC connection was applied.

The FCTC connection configuration is detailed in Table 1.

Table 1. FCTC connection configuration
Source CHPID on LPAR1	FCTC device numbers	Target CHPID on LPAR2
`3C`	`D000-D00F`	`3C`
`3D`	`D010-D01F`	`3C`
`3E`	`D020-D02F`	`3C`
`3C`	`D040-D04F`	`3D`
`3D`	`D050-D05F`	`3D`
`3E`	`D060-D06F`	`3D`
`3C`	`D080-D08F`	`3E`
`3D`	`D090-D09F`	`3E`
`3E`	`D0A0-D0AF`	`3E`

The set of 144 possible FCTC connections presented in Table 1 is the superset that is available for the z/VM® configuration of the ISFC logical link connecting the two z/VM members running in the LPARs. The IOCDS configuration reflected in Figure 3 and Table 1 was used for our tests unless otherwise noted.

In addition, a “striping” approach was applied for some test cases. In this case, FCTC device numbers were not assigned in contiguous ranges, but in a cyclic manner, as shown in Table 2.

Table 2. “FCTC connection configuration with "striped" device numbers
Source CHPID on LPAR1	FCTC device numbers	Target CHPID on LPAR2
`3C`	`D000, D003, D006, D009, D00C`	`3C`
`3D`	`D001, D004, D007, D00A, D00D`	`3D`
`3E`	`D002, D005, D008, D00B, D00E`	`3E`

If the “striped” IOCDS configuration reflected in Table 2 was used for a particular test, this is specifically noted.

Finally, a second FICON Express4 channel card was temporarily available for additional tests. The four FICON channels on that card had the CHPID numbers 4A, 4B, 4C and 4D. The IOCDS configuration for this card was done similar to that shown in Table 1, using device numbers D600 to D6FF. In addition, an alternative “striped” IOCDS configuration similar to that shown in Table 2 was used for some tests.

A further IOCDS variant was the addition of 16 more FCTC device number for CHPID 3C, with FCTC device numbers D700-D70F, such that FCTC devices from CHPID 3C were defined at both the low and the high end of the device number range.