Resource management overview

In a typical VMware vSphere environment, many VMs run simultaneously on the same ESXi host and resource contention can occur. For proper resource management, vSphere offers a set of mechanisms designed to guarantee access to resources when necessary, to curb or control the use of resources, and to enable prioritized access to resources. The three mechanisms that control a VM’s access to a given resource are:

• shares – specify the relative priority of a VM’s access to a given resource. If an ESXi host comes under contention and must decide which VM gets access to which resources, VMs with higher shares assigned will have higher priority, and therefore greater access, to the ESXi host’s resources.
• limits – restrict the amount of a given resource that a VM can use. Examples are maximum consumption of CPU cycles or host physical memory. This option is used to prevent a virtual machine from using more resources than specified.
• reservations – specify a specific amount of the resource for the virtual machine. This option is used to guarantee a minimum allocation of CPU and memory for a virtual machine. A VM will start only if its reservation can be guaranteed.