Your customer is running a NetApp AFF A800 system with NetApp ONTAP 9.

 According to the NetApp Knowledge Base, adding a second NS224 shelf to an existing stack can cause the first shelf ID to change to the serial number if the cables are not connected properly1. This can also result in a Medium Impact error message: Shelves with both connections via the same SAS path detected2. This situation is not normal for a NetApp AFF A800 system andcan affect performance and availability. The cables should be reconnected according to the SAS cabling rules and concepts for shelves with IOM12/IOM12B modules3 and the controller-to-stack cabling worksheet template for quad-pathed connectivity4. References = Shelves with both connections via the same SAS path detected, Adding a second NS224 shelf, changes first shelf ID to the serial number, SAS cabling rules and concepts - shelves with IOM12/IOM12B modules, Controller-to-stack cabling worksheet template for quad-pathed connectivity.