There's an internal document for the upgrade process, but there's the following note in the 8.0 Cluster release notes:
'Customers upgrading from Data ONTAP GX 10.x must follow an assisted upgrade process. Contact your support representative before attempting to upgrade to Data ONTAP 8.0 Cluster-Mode'
While moving from Data ONTAP GX to Data ONTAP 8.0 Cluster-Mode requires a reboot, all data can be maintained.
Upgrade from 8.0 to 8.0.1 is covered in the Data ONTAP® 8.0.1 Cluster-Mode Upgrade Guide.
I hope this response has been helpful to you.
At your service,
Eugene Kashpureff
NetAppU Instructor and Independent Consultant
(P.S. I appreciate points for helpful or correct answers.)