I have a FAS3210A with 2 DS4243s, with each controller owning all the disks in a particular shelf. I need to reset one controller back to factory defaults to address some RG misconfiguration and set my root aggr to 64-bit, and have already migrated all data off the controller in preparation for this task. The other controller and its disks still contain production data, so I need to tread very carefully. I suspect that option 4 will only initialize the disks owned by that particular controller and leave the remaining disks visible via MPHA untouched but would like some confirmation of this. Would it be a good precaution to remove this controller's visibility to the other disks by disconnect the SAS cabling to the other shelf or should that be unnecessary?
Normally it will touch only disks owned by this controller. I have never seen it to do anything different. But of course if you can, physically separating other disks during installation won't do any harm.
Any disks owned by the controller you are running 4/4a on will be be initialized and a 3 of them will be chosen to create an aggregate and add a root volume. Don't forget to reinstall Data ONTAP so the new root volume gets all the AutoSupport and GUI related support files installed.