For a troubleshooting standpoint, we might be putting nodes in maintenance mode (MM) and rebooting for any specific task, but when we are working on a vSAN enabled cluster we need to make sure it will support entering in maintenance mode in a timely manner to apply whatever action we desire to apply.

Here is where the new feature enhancement to vSAN Maintenance Mode workflow called Data Migration Pre-Check jumps to the rescue. – Introduced on 6.7 U3

This feature performs a cluster-wide impact assessment of a host entering maintenance mode. This assessment dramatically helps us to make informed decisions while planning our maintenance activities.

 

Keep in mind that with vSAN, each host in the cluster contributes to the capacity and thereby has data stored in the local physical drives. While moving a host to MM, you must decide if data needs to be migrated or retained. Also, if data needs to move, you have to ascertain the type and amount of data that needs to move.

Before you place a vSAN host into maintenance mode, run the data migration pre-check. The test results provide information to help you determine the impact to cluster capacity, predicted health checks, and any objects that will go out of compliance. If the operation will not succeed, pre-check provides information about what resources are needed.

Steps:

  1. Navigate to the vSAN cluster.
  2. Click the Monitor tab.
  3. Under vSAN, click Data Migration Pre-check.
  4. Select a host, a data migration option, and click Pre-check.
    vSAN runs the data migration precheck tests:

The pre-check results show whether the host can safely enter maintenance mode.

  • The Object Compliance and Accessibility tab display objects that might have issues after the data migration.
  • The Cluster Capacity tab displays the impact of data migration on the vSAN cluster before and after you perform the operation.
  • The Predicted Health tab displays the health checks that might be affected by the data migration.

 

If you want to see how this is performed, please follow this demonstration

 

Hope this is useful,
Jorluis

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