He's suggesting you pull 1 drive breaking the RAID, then raid the two drives in the new enclosure and copy the files across.
You could do this with just 2 drives.
Break RAID A.
Move 1 drive to RAID B.
Copy from A to B.
Move drive 2 to RAID B.
Repair RAID B.
Theres no (R)edundency while you do this.