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Analysis of I/O rates detected one or more control units with an exception.


CHECK(IBMIOS,IOS_IORATE_MONITOR) determined that one or more control units had inconsistent I/O rates across the paths of the subsystem.

Typically, I/Os are distributed equally across all paths for a control unit. When the system determines that there is a performance problem with a path, it will direct I/Os away from that path. This action, taken by the system to correct the performance problem, results in inconsistent I/O rates across the paths.

Each of the control units in the report had a total I/O rate across all channel paths that exceeded the THRESHOLD parameter value, and had at least one path whose I/O rate was significantly lower (as defined by the RATIO parameter value) than the rate for the path with the highest I/O rate. That is, the I/O rate for the path with the highest I/O rate was at least 'ratio' times higher than that of the lowest I/O rate for this control unit. This may happen when there is a problem somewhere in the fabric, such as, hardware errors, I/O mis-configurations, or congestion. Each of the paths identified with the lower I/O rates should be further examined to determine the source of the problem.

For example, with a THRESHOLD value of 100 I/Os per second and a RATIO value of 2, this message will be issued when at least one control unit in the system had a total I/O rate for all of its channels exceeding 100 I/Os per second, and there was one or more paths with an I/O rate less than half that of the path with the highest I/O rate.

  • If parameters have recently been changed, this result may be based on previously defined parameters. Newly updated parameter values will be used the next time control unit data is gathered.
  • For more information on setting the THRESHOLD and RATIO parameters, see the section on 'IOS_IORATE_MONITOR' in IBM Health Checker for z/OS User's Guide.

System action

The system continues processing

Operator response

Contact the System Programmer.

System programmer response

Refer to the corresponding reports for this Health Check to determine which control units and channel paths have delays. Use diagnostic tools (such as the Resource Monitoring Facility (RMF), the D M=DEV,ROUTE= console command, or hardware diagnostics) to help determine the source of the problem.

Problem determination






Routing code

See note 35.

Descriptor code

3 is the default set by this check. See note 1.



Reference Documentation


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