The key element in effecting optimum workload balance is appropriately setting the policies that determine when alerts are fired to signal that performance issues are detected. And the issues can be alleviated through a rebalance of system resources. For information on setting policies in vRealize Operations Manager see the following:
Key among a number of settings relevant to the cluster workload are acceptable demand for CPU and memory. Diskspace demand is not considered as part of the workload balance equation.
In setting policies at the Add/Edit Monitoring Policy workspace, you arrive at a workload score that determines when demands on computing and memory are within an acceptable zone (green), moving toward contention (orange) or unacceptably high (red).
If a cluster CPU or memory utilization has reached the maximum configured capacity, there is no room left to move compute resources, and rebalancing is not possible. Set workload scores to values that trigger an alert well before absolute maximum capacity is reached.
Cluster Headroom Policy and Storage vMotion
The Add/Edit Monitoring Policy workspace includes additional options that more generally define how and when rebalance actions occur: click Workload Automation Details to set Balance, Consolidate, Headroom and Advanced Settings.
The Headroom option can potentially act more directly on rebalancing actions than the Balance or Consolidate workload options, because it sets a value that directly impacts the cluster workload limit policy. Headroom sets a buffer, that is, a workload limit separate from the workload score you defined as within the green zone in your policy settings. If your headroom buffer is, for example, 20 percent, the workload limit is effectively 80 percent, even if you set a workload score in the policy settings that permits the green zone to reach 90 percent. When Workload Balance calculates a rebalancing plan, it abides by the more restrictive metric.
Under Advanced Settings, you must ensure Storage vMotion is set to ON - the default.