Hosts and DRS clusters are providers of CPU and memory resources, and VMs are consumers of CPU and memory resources. For a DRS cluster, the vCenter Server manages all of the CPU and memory of all of the hosts in the cluster.

Use the vSphere Client and vCenter Server to check a VM’s Resource Allocation tab for the appropriate amount of CPU and memory. Check the shares, reservation and limit settings for the VM. Ensure that the limit setting is Unlimited (default).

Through testing and experience, and by analyzing esxtop data, you can determine the appropriate level of shares and reservation for a VM. Shares and reservation take effect only when not enough resources are available to meet the needs of all the VMs on a particular ESX host.

To change the share-based percentage of the total CPU or memory for a VM, or to change the guaranteed reservation of the CPU or memory for a VM, select the VM’s Edit Settings tab, then the Resources tab, and then make your changes.

Configure an adequate reserve of CPU and memory resources so that the VM is not spending much ready wait time. Ready wait time, or just “ready wait” or “ready time,” is the time that a VM waits in a ready-to-run state before it can be scheduled on a CPU.