The Max concurrent power operations setting governs the maximum number of concurrent power operations that can occur on remote desktop virtual machines in a vCenter Server instance. This limit is set to 50 by default. You can change this value to support peak power-on rates when many users log on to their desktops at the same time.
As a best practice, you can conduct a pilot phase to determine the correct value for this setting. For planning guidelines, see "Architecture Design Elements and Planning Guidelines" in the Horizon 7 Architecture Planning document.
The required number of concurrent power operations is based on the peak rate at which desktops are powered on and the amount of time it takes for the desktop to power on, boot, and become available for connection. In general, the recommended power operations limit is the total time it takes for the desktop to start multiplied by the peak power-on rate.
For example, the average desktop takes two to three minutes to start. Therefore, the concurrent power operations limit should be 3 times the peak power-on rate. The default setting of 50 is expected to support a peak power-on rate of 16 desktops per minute.
The system waits a maximum of five minutes for a desktop to start. If the start time takes longer, other errors are likely to occur. To be conservative, you can set a concurrent power operations limit of 5 times the peak power-on rate. With a conservative approach, the default setting of 50 supports a peak power-on rate of 10 desktops per minute.
Logons, and therefore desktop power on operations, typically occur in a normally distributed manner over a certain time window. You can approximate the peak power-on rate by assuming that it occurs in the middle of the time window, during which about 40% of the power-on operations occur in 1/6th of the time window. For example, if users log on between 8:00 AM and 9:00 AM, the time window is one hour, and 40% of the logons occur in the 10 minutes between 8:25 AM and 8:35 AM. If there are 2,000 users, 20% of whom have their desktops powered off, then 40% of the 400 desktop power-on operations occur in those 10 minutes. The peak power-on rate is 16 desktops per minute.