You can change the virtual machine memory configuration to improve virtual machine performance across your data center. You can set most of the memory parameters during virtual machine creation or after the guest operating system is installed. Most changes require that you power off the virtual machine first.

Minimum memory size is 4MB for virtual machines that use BIOS firmware. Virtual machines that use EFI firmware require at least 96MB of RAM or they cannot power on.

Maximum memory size for a virtual machine depends on the host's physical memory and the virtual machine's compatibility setting.

If the virtual machine memory is greater than the host memory size, swapping occurs, which can have a severe effect on virtual machine performance. The maximum for best performance represents the threshold above which the host’s physical memory is insufficient to run the virtual machine at full speed. This value fluctuates as conditions on the host change, for example, as virtual machines are powered on or off.

The memory size must be a multiple of 4MB.

Table 1. Maximum Virtual Machine Memory

Introduced in Host Version

Virtual Machine Compatibility

Maximum Memory Size

ESXi 6.7

ESXi 6.7 and later

6128GB

ESXi 6.5

ESXi 6.5 and later

6128GB

ESXi 6.0

ESXi 6.0 and later

4080GB

ESXi 5.5

ESXi 5.5 and later

1011GB

ESXi 5.1

ESXi 5.1 and later

1011GB

ESXi 5.0

ESXi 5.0 and later

1011GB

ESX/ESXi 4.x

ESX/ESXi 4.0 and later

255GB

ESX/ESXi 3.x

ESX/ESXi 3.5 and later

65532MB

The ESXi host version indicates when support began for the increased memory size. For example, the memory size of a virtual machine with ESX/ESXi 3.5 and later compatibility running on ESXi 5.0 is restricted to 65,532MB.

Prerequisites

  • Power off the virtual machine.

  • Verify that VMware Tools is installed.

Procedure

  1. Right-click a virtual machine in the inventory and select Edit Settings.
  2. Make changes to the following settings and click OK.

    Option

    Description

    RAM

    In the RAM text box, type the amount of RAM to assign to the virtual machine or select one of the suggested values from the drop-down menu.

    Reservation, Limit, Shares

    A virtual machine has the following user-defined settings that affect its memory resource allocation.

    • Limit: Upper limit for this VM's memory allocation. Select Unlimited to specify no upper limit.

    • Reservation: Guaranteed memory allocation for this VM

    • Shares: Memory shares for this VM in relation to the parent's total. Sibling virtual machines share resources according to their relative share values, bounded by the reservation and limit. Select Low, Normal, or High, which specify share values in a 1:2:4 ratio. Select Custom to give each VM a specific number of shares, which express a proportional weight.

    See the vSphere Resource Management documentation for details.