- IOS=xx
- The two alphanumeric characters (xx) are appended to IECIOS to identify the IECIOSxx parmlib member. If the IOS parameter is not specified, the system uses defaults for MIH processing, defaults for hot I/O, and defaults for IOS CTRACE processing.
To change the IECIOSxx member after initialization, you can specify the SET IOS=xx command. The SET IOS=xx command changes the I/O timing limits, MIH intervals and FICON® statistics option. It does not, however, change the values initialized for hot I/O detection and it does not change the current IOS CTRACE options. Changing the hot I/O detection or recovery values requires a reIPL. Changing the CTRACE parmlib member or options requires the use of the TRACE operator command. For a description of the TRACE operator command, see z/OS MVS System Commands.
You can change the FICON,
STORAGE, CAPTUCB, MIDAW, HYPERPAV, 
HYPERWRITE,
EKM,
RECOVERY, and ZHPF parameters dynamically using the SETIOS command.
See z/OS MVS System Commands.