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There are several reasons the Distributed Resource Scheduler might not suggest load-balancing recommendations for your VMware vSphere cluster. It could be because it has no recommendations to give, but it could also be an issue with your settings.
If your cluster runs for a while and you never see any DRS load-balancing recommendations, it might be a good thing. If all of your virtual machines receive all the resources they need, then there is no congestion in resource usage. The DRS does not need to take action. You can enjoy your properly load-balanced vSphere cluster.
Another reason you might not see any DRS load-balancing recommendations, even if there is resource congestion, is that you might have configured the cluster automation level to the most restrictive level. Many IT administrators have never noticed the text that accompanies the slider in the web interface where you can choose a more aggressive or conservative setting for DRS.
In the most conservative setting, DRS only offers recommendations when you place a cluster in maintenance mode or when the vSphere cluster must enforce affinity or anti-affinity rules. The text with the default setting where the slider is in the middle -- Figure A -- shows that vSphere will implement DRS load-balancing recommendations to improve the cluster's load balance.
If you set the slider to the most conservative setting, it does not mean that DRS is conservative in its recommendations. It means that only the DRS load-balancing recommendations that are necessary for constraints and host maintenance will be applied.
This difference is often misinterpreted or misunderstood -- or missed altogether -- and can lead to unbalanced clusters. To solve that, select a slider position from level 2 through 5. Alternatively, you could just leave it at the default, which is the best setting for most environments.
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