We currently have a FAS2040 dual controller (active/active) with an external shelf that contains all the disks in the system. I'm looking to add 12 SATA disks to the head unit and wanted to know some recommendations for the disk assignments. For the current disks, 1/2 the disks are owned by controller A and 1/2 the disks are owned by controller B. Is this how it should be configured? Isn't there alot of wasted disks in this configuration? Would it be better to have all the disks owned by one of the controllers?
It's all a matter a preference really. Whether you want to have an active-active vs active-standby. Yes, an active/active configuration requires more disks, because of the additional aggregate and raid groups, however both controllers are actively utilized.
Keep in mind that even if you want to assign all disk to a one of the heads/controller you can't, the standby head/controlle still needs to have a root volume, aggregate and thefore raid group in order to boot ONTAP.