Performance Best Practices for VMware vSphere, Part 5

ESXi and Virtual Machines

ESXi General Considerations

This subsection provides guidance regarding a number of general performance considerations in ESXi.

• Plan your deployment by allocating enough resources for all the virtual machines you will run, as well as those needed by ESXi itself.
• Allocate to each virtual machine only as much virtual hardware as that virtual machine requires. Provisioning a virtual machine with more resources than it requires can, in some cases, reduce the performance of that virtual machine as well as other virtual machines sharing the same host.
• Disconnect or disable any physical hardware devices that you will not be using. These might include devices such as:

?? COM ports

?? LPT ports

?? USB controllers

?? Floppy drives

?? Optical drives (that is, CD or DVD drives)

?? Network interfaces

?? Storage controllers

Disabling hardware devices (typically done in BIOS) can free interrupt resources. Additionally, some devices, such as USB controllers, operate on a polling scheme that consumes extra CPU resources. Lastly, some PCI devices reserve blocks of memory, making that memory unavailable to ESXi.

• Unused or unnecessary virtual hardware devices can impact performance and should be disabled. For example, Windows guest operating systems poll optical drives (that is, CD or DVD drives) quite frequently. When virtual machines are configured to use a physical drive, and multiple guest operating systems simultaneously try to access that drive, performance could suffer. This can be reduced by configuring the virtual machines to use ISO images instead of physical drives, and can be avoided entirely by disabling optical drives in virtual machines when the devices are not needed.
• ESXi 6.7 introduces virtual hardware version 14. By creating virtual machines using this hardware version, or upgrading existing virtual machines to this version, a number of additional capabilities become available. This hardware version is not compatible with versions of ESXi prior to 6.7, however, and thus if a cluster of ESXi hosts will contain some hosts running pre-6.7 versions of ESXi, the virtual machines running on hardware version 14 will be constrained to run only on the ESXi 6.7 hosts. This could limit vMotion choices for Distributed Resource Scheduling (DRS) or Distributed Power Management (DPM).

Reference:

Performance Best Practices for VMware vSphere 6.7, July 27, 2018