VMware DRS Stars

I get this question a lot from clients “In VMware DRS what is a star? what percentage of CPU/memory equals a star?” I also have wonder what makes a star and how is a star calculated.

My usual response is that a star is calculated by some DRS algorithm and that there is no exact answer to what a star is. I have never really found anything that explains how starts are calculated. The closest thing I have found is in the VMware DRS white paper http://download3.vmware.com/vmworld/2006/mdc9694.pdf

• Level 1 – Apply only five-star recommendations. Includes recommendations that must be
followed to satisfy cluster constraints, such as affinity rules and host maintenance. This level
indicates a mandatory move, required to satisfy an affinity rule or evacuate a host that is
entering maintenance mode.

• Level 2 – Apply recommendations with four or more stars. Includes Level 1 plus
recommendations that promise a significant improvement in the cluster’s load balance.

• Level 3 – Apply recommendations with three or more stars. Includes Level 1 and 2 plus
recommendations that promise a good improvement in the cluster’s load balance.

• Level 4 – Apply recommendations with two or more stars. Includes Level 1-3 plus
recommendations that promise a moderate improvement in the cluster’s load balance.

• Level 5 – Apply all recommendations. Includes Level 1-4 plus recommendations that
promise a slight improvement in the cluster’s load balance.

If anyone out there has some more detailed information on how a start is calculated in DRS I would love to see it.

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