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Performance diagnostics in vSAN reports: "The outstanding IOs for the benchmark might not be optimal to achieve the desired goal (2150017)

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In the vSAN performance diagnostics, you see this message:

The outstanding IOs for the benchmark might not be optimal to achieve the desired goal.


This message implies that the outstanding IOs are either very  low or high for the desired goal. The outstanding IOs should be high (ideally at least 2 per host) for maximum IOPS and maximum throughput, else the system is bottlenecked by the time it takes to process IOs. Alternately, outstanding IOs should be low (ideally 1 per host) for minimum latency, else the IOs may queues at different layers leading to higher latency.

The detailed graphs explain how this error is detected. The graphs may show the plot of outstanding IOs at the vSAN –VMs level (i.e. outstanding IOs  across the vSAN cluster) and compare against an expected threshold. The detailed graphs may also show the “Delayed IO Percentage” or the “Delayed IO Latency” at the vSAN diskgroup layer and compare against expect threshold.   


To resolve this issue, adjust the outstanding IOs according to the desired goal of performance evaluation. 

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