For a NetApp AFF All SAN Array (ASA) A800 MetroCluster IP configuration with 72 disks per site and Cisco N9K-C9336C-FX2 backend switches, the minimum number of rack units required on each site is 16 RU. This includes space for the controllers, disk shelves, and the necessary network switches. This configuration ensures that all components are properly accommodated and operational within the specified rack space.

For detailed information on the rack unit requirements and MetroCluster IP configurations, refer to:

NetApp Documentation on MetroCluster IP

MetroCluster IP Solution Architecture