ALR0525W The Write-cache Delay Percentage of controller or node controller or node name in storage system storage system name was measured to be measured value%, which violated the warning-stress boundary value of boundary value%.
Explanation
Write-cache Delay Percentage measures the approximate percentage of I/O operations that were delayed due to write-cache space constraints or other conditions on the controllers and nodes in monitored storage systems. This value represents the average percent of all I/O operations that experienced delays. A threshold was defined on this metric, which causes the measured value to be compared to the defined boundaries for each set of performance statistics collected from the storage system.
This message indicates that a threshold boundary violation occurred. In this case, the specified controller or node in the storage system has a Write-cache Delay Percentage value that is greater than or equal to the warning-stress boundary, but less than the critical-stress boundary that was defined for the related threshold.
Action
The threshold violation might indicate that a performance problem exists for this controller or node. Either the amount of cache installed on the controller or node is insufficient to handle its workload, or the controller or node is experiencing a hardware or software related problem that is causing cache slots to be occupied longer than necessary due to a drop in write performance, or the controller or node is being overwhelmed with too high a write workload. If the workload is too high, moving some of the controller's or node's workload to other less busy controllers or nodes might resolve the problem.
However this threshold indication is only as good as its defined boundary values. If the specified boundary value is too low, IBM Spectrum Control might recognize many violations, even though there is really no underlying performance problem with the controller or node. In this case, increase the boundary value in the threshold definition to reduce the number of unnecessary alerts.
Note there may be cases when the Write-cache Delay Percentage is high but the total number of delayed I/O operations is very low. Such cases are generally not a cause for concern, because application performance will rarely be affected due to the low I/O rates. To avoid unnecessary threshold alerts for such cases, consider enabling the Write-cache Delay I/O Rate filter. Use this filter to ignore any violations of the Write-cache Delay Percentage threshold for controllers or nodes with very low I/O rates.