I have one 12 TB mirror (2*12 TB) in my 4-bay FreeNAS.
The pool is full, how would I expand the capacity?
Can I add another mirror and stripe both to get 24 TB of total storage? (or would that erase my existing data?)
You would need another RAID1 Array so refer to whatever your using for that RAID Array management to see if the solution your using (Software,Hardware RAID Card, etc) support more than one RAID Array.