You need to reboot your second controller, and go to maintenance mode to re-install your base system.
You could also create a new aggregate with the 2 spare drives and move the vol0/root volume to it, but it is harder to perform.
On your second HA controller :
- disable HA with cf disable
- go to maintenance mode using CTRL-C
- reinstall the system (using the right option which is "install a new system" I guess, I'm not completely sure.