vC Ops : Using vC Ops to get a Cluster Optimal HA Slot Size

I have been thinking about this for a while now….using vC Ops stats to get a more realistic value for HA slot sizes. To recap on a HA Slot Size :

A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster.

(Source :

So how can I get the Avg CPU and Memory Resource from vC Ops ? Well we have a Report that you can run on a Cluster that will give you the Avg CPU and Memory Demand of a VM. See screenshot below :

When you run this report you will get an output that looks as follow in section 1.3 :

There is a few Metric’s to use. I would Recommend to use Effective Memory. The diffidence between Limited and Effective is as follow :

  • Limited : This is an avg of demand for resources
  • Effective : Is the same as Limited until “Consider Stress” is enabled. Then we look at the Peak values.

For my Cluster then I would consider setting a Slot size of the following, taking Deviation into account :

  • CPU : 180-300Mhz
  • Mem : 370-415MB


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