Before you shut down, reboot, or disconnect a host that is a member of a vSAN cluster, you must place the host in maintenance mode. When you place a host in maintenance mode, you must 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.

Prerequisites

Verify that your environment has the capabilities required for the option you select.

Procedure

  1. Right-click the host and select Maintenance Mode > Enter Maintenance Mode.
  2. Select a data evacuation mode and click OK.
    Option Description
    Ensure accessibility This is the default option. When you power off or remove the host from the cluster, vSAN ensures that all accessible virtual machines on this host remain accessible. Select this option if you want to take the host out of the cluster temporarily, for example, to install upgrades, and plan to have the host back in the cluster. This option is not appropriate if you want to remove the host from the cluster permanently.
    Typically, only partial data evacuation is required. However, the virtual machine might no longer be fully compliant to a VM storage policy during evacuation. That means, it might not have access to all its replicas. If a failure occurs while the host is in maintenance mode and the Primary level of failures to tolerate is set to 1, you might experience data loss in the cluster.
    Note: This is the only evacuation mode available if you are working with a three-host cluster or a vSAN cluster configured with three fault domains.
    Full data migration vSAN evacuates all data to other hosts in the cluster and maintains the current object compliance state. Select this option if you plan to migrate the host permanently. When evacuating data from the last host in the cluster, make sure that you migrate the virtual machines to another datastore and then place the host in maintenance mode.

    This evacuation mode results in the largest amount of data transfer and consumes the most time and resources. All the components on the local storage of the selected host are migrated elsewhere in the cluster. When the host enters maintenance mode, all virtual machines have access to their storage components and are still compliant with their assigned storage policies.

    Note:

    If there are objects in reduced availability state, this mode maintains this compliance state and does not guarantee that the objects will become compliant.

    If a virtual machine object that has data on the host is not accessible and is not fully evacuated, the host cannot enter maintenance mode.
    No data migration vSAN does not evacuate any data from this host. If you power off or remove the host from the cluster, some virtual machines might become unaccessible.
    A cluster with three fault domains has the same restrictions that a three-host cluster has, such as the inability to use Full data migration mode or to reprotect data after a failure.

    Alternatively, you can place a host in the maintenance mode by using ESXCLI. Before placing a host in this mode, ensure that you powered off the VMs that run on the host.

    To enter maintenance mode, run the following command on the host:

    esxcli system maintenanceMode set --enable 1

    To verify the status of the host, run the following command:

    esxcli system maintenanceMode get

    To exit maintenance mode, run the following command:

    esxcli system maintenanceMode set --enable 0

What to do next

You can track the progress of data migration in the cluster. See "Monitoring the Resynchronization Tasks in the vSAN Cluster" in vSAN Monitoring and Troubleshooting.