You must monitor the average I/O elapsed time for read I/O and write I/O. A high average I/O elapsed time indicates that I/O contention is occurring. The requested I/O is accessing data from a busy data set, volume, or control unit and is continually being suspended.
For a volume or control unit level I/O problem, use the MVS performance management component to determine which component in the path is the bottleneck. If the problem is at this level, the MVS system programmers should be involved.
High average I/O elapsed times ...