Before you shut down, reboot, or disconnect a host that is a member of a Virtual SAN 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 Virtual SAN cluster enters maintenance mode, the cluster capacity is automatically reduced, because the member host no longer contributes capacity to the cluster.
Verify that your environment has the capabilities required for the option you select.
- Right-click the host and select Maintenance Mode > Enter Maintenance Mode.
- Select a data evacuation mode and click OK.
This is the default option. When you power off or remove the host from the cluster, Virtual SAN 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 permanently remove the host from the cluster.
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. In case of a failure while the host is in maintenance mode and the Number 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 Virtual SAN cluster configured with three fault domains.
Full data migration
Virtual SAN evacuates all data to other hosts in the cluster, maintains or fixes availability compliance for the affected components, and protects data when sufficient resources exists in the cluster. Select this option if you plan to migrate the host permanently. When evacuating data from the last host in the cluster, make sure 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 of the components on the local storage of the selected host will be migrated elsewhere in the cluster so that when the host enters maintenance mode, all virtual machines will have access to their storage components and will still be compliant to their assigned storage policies.Note:
If a virtual machine object that has data on the host is not accessible and is not fully evacuated, the host will be unable to enter the maintenance mode.
No data migration
Virtual SAN 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.
What to do next
You can track the progress of data migration in the cluster. See Monitor the Resynchronization Tasks in the Virtual SAN Cluster.