Oracle Exadata Storage Server X6-2 High Capacity Installation Manual page 23

Exadata Storage Expansion Rack X6-2 Configuration Restrictions
3. Up to 7 storage servers in U27 to U40, starting with U27.
4. Up to 2 storage servers in U26 to U23, starting with U26.
5. Up to 2 storage servers in U19 to U16, starting with U19.
6. 1 storage server in U41 to U42.
About Rack Installation 23