Understanding resource controls

An administrator can customize the amount of resources allocated to a virtual machine or to the resource pool in which those virtual machines reside by modifying resource controls. Each of the primary four resources (CPU, memory, network, and storage) can be controlled, but network and storage require the use of the advanced features of Network I/O Control or Storage I/O Control, respectively. There are three resource controls that are available to determine how resources are provided to a virtual machine, these are: shares, limits, and reservations. When an ESXi host's memory or CPU resources are overcommitted, a virtual machine's allocation target is somewhere between its specified reservation and specified limit, depending on the VM's share and the system load. This is something that we will explore later on in this chapter.

Shares

A share is a value that specifies the relative priority or importance of a virtual machine (or resource pool...