Home > Storage > PowerMax and VMAX > Storage Admin > Dell PowerMax and VMware vSphere Configuration Guide > vSphere Storage I/O Control
It is possible to change the Congestion Threshold, which is the value at which VMware begins implementing the shares and IOPS settings for a VM. By default, VMware dynamically determines the best congestion threshold for each device. VMware determines the peak latency value of a device, and then sets the threshold of that device to 90% of that value. This operation is shown in Figure 118. For example, a device that peaks at a 10 ms have its threshold set to 9 ms. The user can change the percent amount within the vSphere Client.
Figure 123 demonstrates how the percentage can be changed to anything between 50% to 100%. Alternatively, a manual millisecond threshold can be set between 5 ms to 100 ms. Dell Technologies recommends using the default value. Doing so allows VMware to dynamically control the congestion threshold, rather than using a manual millisecond setting. A different percent amount is perfectly acceptable if wanted.
If an attempt is made to adjust the threshold to a manual setting, VMware warns the user about the consequences as seen in Figure 124.