I recently had a customer in a POC that thought the Cluster Capacity dashboard was showing some additional VM headroom numbers that were too good to be true. When we investigated further by taking our mouse and hovering over the name of the cluster in the Summary table of the Cluster Capacity dashboard, we could see that the default template that was chosen was a smaller VM configuration with low utilization. The important factor to remember is that the calculation of VM headroom is made off of BOTH the Allocation (VMem, VCPU, etc) and the utilization of those commodities.
Fortunately, our engineering team has made this pretty easy to change the templates used for this analysis, here's how.
The Cluster Capacity Dashboard is a default view right off of the Dashboard tab and answers the question, given the available capacity of the environment, current and past workload demand, how much headroom do I have to run additional workload (as represented by a template).
To change this just go to Policy tab, then down to Cluster Capacity
You have the option now of changing the template to be used as the default Global setting for the entire environment, or on a Per Cluster basis. For most customers I'm talking with today a good Global template is a Server 2012 R2 configuration that we've imported from vCenter. If you don't have an imported template you want to use go ahead and select the Template Catalog button and create a new one from within VMTurbo. Don't forget to hit Apply. Note that these templates by default will have an assumed 70% utilization of the VMem, 50% utilization of VCPU, and 100% of VStorage. Remember it is not the size of the VM's allocated resources, but the utilization of those resources, that drives the headroom analysis.
If you have specific clusters with a different type of workload that is commonly deployed, then expand the navigation tree at Cluster Capacity, and select Host. Then choose a cluster to modify. By customizing per cluster you can then address multiple scenarios such as 1) a SQL cluster that has larger machines requiring a specific template, 2) there is a VDI cluster that uses a smaller template, or 3) differentiating the capacity in Production vs Development Clusters that have different average VM types. Use the Override check box and the settings to customize to your desire.
Now it's time to wait and let VMTurbo do its magic. Note that the Cluster Capacity analyses are run overnight at the rate of 10 clusters per run.