btrfs yes
raid 5 3 usable 1 protection can lose 1 drive
raid 6 1 usable 1 protection can lose 2 drives
use raid calculator
DS920+
https://www.youtube.com/watch?v=8cBpAbh5EGw
My user files sizes
186 GB Office
7 GB One QB files
36 GB One User Files Including QB files
GB Four Files
GB Basement Files
200 GB User Predator Files
35 GB Ebooks Predator Files
1 GB Audio Books Predator Files
GB Florida Files