• A higher value typically results in higher aggregate throughput and weaker isolation. Throttling will not occur unless the overall average latency is higher than the threshold
• If throughput is more critical than latency, do not set the value too low. For example, for Fibre Channel disks, a value below 20 ms could lower peak disk throughput. On the other hand, a very high value (above 50 ms) might allow very high latency without any significant gain in overall throughput.
• A lower value will result in lower device latency and stronger virtual machine I/O performance isolation. Stronger isolation means that the shares controls are enforced more often. Lower device latency translates into lower I/O latency for the virtual machines with the highest shares, at the cost of higher I/O latency experienced by the virtual machines with fewer shares.
• If latency is more important, a very low value (lower than 20 ms) will result in lower device latency and better isolation among IOs at the cost of a decrease in aggregate datastore throughput.

Procedure

1. Select a datastore in the vSphere Client inventory and click the Configuration tab.
2. Click Properties.
3. Under Storage I/O Control, select the Enabled check box.
4. Click Advanced to edit the congestion threshold value for the datastore. The value must be between 10 and 100. You can click Reset to restore the congestion threshold setting to the default value (30 ms).
5. Click Close.