My question might be confusing so please try to understand the specific need
I have a backup and archiving system which work well.
I am a bit paranoid, so I bought in addition My Book Duo which I want to connect to a computer for local backup daily (but manually)
RAID isn’t a backup, but in this case if I copy data from my PC to the My Book, then it will sync to the other disks (not sure if at real time or not)
The other option is to manually copy from one disk to another (rsync or what ever)
Which way would be more reliable in terms of data loss? (Ignore the fact of power loss please)