how much consolidation can occur. Your Power Optimization thresholds should be set
higher than those for Dynamic Optimization. The goal of Power Optimization is to
consolidate in quiet times, and if the Power Optimization thresholds were lower than
the Dynamic Optimization thresholds, then hosts would be powered off and lots of
Live Migrations would occur. VMs would be moved around, and the hosts that were
just powered off would be powered on again. The Power Optimization thresholds also
need to be generous, leaving plenty of spare resources because resource utilization
fluctuates even in quiet times and eventually will pick up again during busy times. It
will take time to power on and boot the servers that were powered down during Power
Optimization times, so plenty of buffer capability is required to ensure no resource
shortage.
Additionally, as Figure 7.40 shows, you can set the times Power Optimization can
occur. In this example, I don’t want Power Optimization to occur during business
hours except for a few exceptions. However, there is no reason to stop Power
Optimization during working hours, provided you set well-defined thresholds to
ensure that hosts have sufficient spare resources and won’t suddenly be overtaxed
during the time it takes to power back on servers that were powered down.