If you still have 3 free disks it's no problem (It's probably best to use RAID 4 + Spare in that case, and remember that the "current" controller still needs at least one spare!)
However, you need a downtime/reboot for this procedure
just do this:
Thank you very much for your reply.
I'm just concerne about the point 5.
I found this documentation "Adding a second controller module to create an HA pair" (https://library.netapp.com/ecm/ecm_download_file/ECMM1280363)
I'm just worried about the point when the system ask to initialize all disks. As the first head is already in production I don't want to lose my data.
Do you have any Advice ?