How to know which IODF file is currently being used?

If for whatever reason you need to know which IODF file is currently being used by the system, just issue the command: D IOS,CONFIG

Example:

D IOS,CONFIG

Returns:

RESPONSE=TST1
IOS506I 10.18.20 I/O CONFIG DATA 118
ACTIVE IODF DATA SET = SYS1.IODF19
CONFIGURATION ID = TEST01         EDT ID = 00
TOKEN:  PROCESSOR DATE     TIME     DESCRIPTION
SOURCE: CMOS03   08-02-19 14:05:33 SYS1     IODF19
ACTIVE CSS:  0    SUBCHANNEL SETS CONFIGURED: 0
CHANNEL MEASUREMENT BLOCK FACILITY IS ACTIVE

As you can see LPAR TST1 is currently using IODF file SYS1.IODF19