If the VMFS3 datastore fails to upgrade, it remains unmounted, and its status changes to Failed to Upgrade. Use the following steps to resolve the failure.
Note: If the upgrade fails in the mixed environment of the 6.5 and 6.7 and later
ESXi hosts, the VMFS3 datastore remains unmounted in the Failed to Upgrade status on the 6.7 host. However, the datastore is accessible from the 6.5 host.