Hi Calvin,
installation best practices in Germany is that you assign the upper shelfs to the upper controller an the bottom to the bottom controller. Best with to seperate stacks. In the real world, especially on small systems with low disk count sometimes the disks in one diskshelf spread to 2 different controller.
If there 2 seperate stacks one controller is owning all of the disks of the stack the disk.auto_assign option is working well. Otherwise you have to assign the disks manually when RMA disks arrived.
Regards
Michael