ALR0704E The I/O Overrun Percentage of port port_name in storage system device_name was found to be measured_value, which violated the defined critical-stress boundary value of boundary_value.
Explanation
I/O Overrun Percentage measures the percentage of I/O operations that had to be discarded by the port because the number of open exchanges exceeded the maximum. This can occur for ports on DS8000 storage systems when the number of open exchanges for the port has reached the maximum value of 2000. This situation can happen when there is too much concurrent I/O being driven to the port. A threshold is defined on this metric, which can be used to compare the value of the I/O Overrun Percentage with the defined boundaries for each set of performance statistics collected from the storage system.
A threshold boundary violation occurred. The specified storage system port has an I/O Overrun Percentage value that is greater than equal to the critical-stress boundary defined for the related threshold.
Action
The threshold violation indicates that the physical capability of the port on the DS8000 system is being exceeded. When an I/O operation is discarded, this usually means that the requesting host server needs to redrive the I/O, which negatively affects the performance of the I/O for the host.
Check the workload of the affected DS8000 system to ensure that it is generally balanced across all the HA ports. If the workload is not balanced across all the ports, try to balance it. Ensure that multipath device drivers are installed and functioning properly on the host servers, so that I/O activity can be spread across multiple DS8000 ports.
If multipath drivers are functioning normally, consider configuring certain ports to allow access from only certain host servers, or consider making zoning changes between host and storage system ports. Sometimes, you might need to change the cabling or the fabric configuration.
If the workload is already balanced and the I/O Overrun Percentage remains high, consider installing more ports in the DS8000 system, or consider moving some of the workload to other storage systems.