Normally all tasks have the same priority when disk I/Os are executed.
An I/O-intensive application with low priority can hinder another, higher-priority application if these application execute I/Os on the same (logical) device. Operations can also be impaired if the I/Os are executed on different (logical) devices which are located on the same physical device or are connected via the same paths, are accessible via the same ports or connected to the same channels.
The IOPT (I/O Priority Handling for Tasks) function enables IORM to detect such conflict situations and to intervene in I/O operation for control purposes. Here IOPT examines both the utilization level of the I/O units (devices, paths, ports and channels) and the I/O priorities of the tasks which use them.
IOPT distinguishes three I/O priorities for tasks:
HIGH (high I/O priority)
MEDIUM (medium I/O priority)
LOW (low I/O priority)
It is possible to assign the task categories (with the exception of SYS) corresponding I/O priorities (IO-PRIORITY attribute) using the following command:
/MODIFY-TASK-CATEGORY IO-PRIORITY=*NONE/*HIGH/*MEDIUM/*LOW
Further information on IORM and IOPT can be found in the “Utility Routines” manual [6 (Related publications)].