Figure 8 Recommended cabling for DD4200 (3TB drives) with Extended Retention Software
With four shelves, two DS60 shelves can have 60 drives each and the other DS60
shelves can only have 15 drives each. It is also possible to configure two full DS60
shelves and one DS60 shelf with 30 drives.
Installing the Shelves
30 Data Domain DS60 Expansion Shelf Hardware Guide