vSphere has long allowed administrators to prioritize virtual machines using a feature called shares. The higher the share level a VM has, the more resources it is allowed to consume when in competition with other VM’s on the same host. Shares is of relative importance to VMs or pools and they apply within the same parent.
One thing to be aware of is shares are only taken into account when there is resource scarcity. So this feature only activates itself when two or more virtual machines compete for resources.
Worth noting too that the actual amount of resources a VM gets may change each time it is powered on. If a host is upgraded with more memory, each virtual machine will get a larger portion of RAM according to the ratio.
To change virtual machine shares, execute the following steps: