Place a Member of vSAN Cluster in Maintenance Mode.
Before shutting down, rebooting, or disconnecting a host that is a member of a vSAN cluster, place the host in maintenance mode. When the host is placed in maintenance mode, select a data evacuation mode, such as Ensure accessibility or Full data migration.
When any member host of a vSAN cluster enters maintenance mode, the cluster capacity is automatically reduced, because the member host no longer contributes capacity to the cluster.
Any vSAN iSCSI targets served by this host are transferred to other hosts in the cluster, and thus the iSCSI initiator are redirected to the new target owner.
Procedure:
Place a host in maintenance mode when it needs service, for example, to install more memory. A host enters or leaves maintenance mode only as the result of a user request.
Virtual machines that are running on a host entering maintenance mode is migrated to another host (either manually or automatically by DRS) or shut down. The host is in a state of Entering Maintenance Mode until all running virtual machines are powered down or migrated to different hosts. You cannot power on virtual machines or migrate virtual machines to a host entering maintenance mode.
When no more running virtual machines are on the host, the host s icon changes to include under maintenance, and the host s Summary panel indicates the new state. While in maintenance mode, the host does not allow deploying or powering on a virtual machine.
Note: DRS does not recommend (or perform, in fully automated mode) any virtual machine migrations off of a host entering maintenance or standby mode if the vSphere HA failover level would be violated after the host enters the requested mode.
The host is in maintenance mode until maintenance mode is exited: select Maintenance Mode > Exit Maintenance Mode.