You place a host in maintenance mode when you need to service it, for example, to install more memory. A host enters or leaves maintenance mode only as the result of a user request.
Before you begin
Before you place a host in maintenance mode, power off all virtual machines that are running on that host or migrate them to another host either manually or automatically by DRS.
About this task
The host is in a state of Entering Maintenance Mode until all running virtual machines are powered off or migrated to different hosts. You cannot power off virtual machines or migrate virtual machines to a host that is entering or in maintenance mode.
To place a host in maintenance mode, all virtual machines that are running on the host must be powered off or migrated to different hosts. If you attempt to place a host that has running virtual machines on it in maintenance mode, DRS must power off or migrate the running virtual machines for the task to complete. If a time out occurs before the virtual machines are powered off or migrated, an error message appears.
When all virtual machines on the host are inactive, the host's icon displays under maintenance and the host's Summary panel indicates the new state. While in maintenance mode, the host does not allow you to deploy or power on a virtual machine.
The host is in maintenance mode until you select Exit maintenance mode.