When backed by auxiliary storage, VIO data set pages can be directed to a subset of the local paging data sets through directed VIO, which allows the installation to direct VIO activity away from selected local paging data sets and use these data sets only for non-VIO paging. With directed VIO, faster paging devices can be reserved for paging where good response time is important. The NONVIO system parameter, with the PAGE parameter in the IEASYSxx parmlib member, allows the installation to define those local paging data sets that are not to be used for VIO, leaving the rest available for VIO activity. However, if space is depleted on the paging data sets that were made available for VIO paging, the non-VIO paging data sets will be used for VIO paging.

The installation uses the DVIO keyword in the IEAOPTxx parmlib member to either activate or deactivate directed VIO. To activate directed VIO, the operator issues a SET OPT=xx command where the xx specifies the IEAOPTxx parmlib member that contains the DVIO=YES keyword; to deactivate directed VIO, xx specifies an IEAOPTxx parmlib member that contains the DVIO=NO keyword. The NONVIO parameter of IEASYSxx and the DVIO keyword of IEAOPTxx is explained more fully in z/OS MVS Initialization and Tuning Reference.