It might not be the cheapest, but 4+1 drives is more efficient than 3+1. Currently I have three 8TB drives: 1xWD Red and 2xIronwolfs (wolves?) with one running as parity (SHR). No complaints. It does everything I need it to do. The interface is simple and everything "just works" as anticipated. If/when I run out of space I plan on adding another 2x8TB drives, probably more ironwolves.
I wouldn't go bigger than 8TB as they already take DAYS to add to the array.
Migrated from a 1512. It took probably about 3-4 days to migrate everything. The new box handled it easily. The old one was struggling a bit with rsync. As the default is ssh with it. Once I had to downgraded the encryption then it went a lot faster (from 30MB to 90MB which was close enough to the limit of the cable to not worry).
918+ here.
The last two drives I put in were 16TBs, and as you say it takes time. It wasn’t helped by me messing the process first round (you need to add the smallest drives first with SHR), so it took over a week.
It might not be the cheapest, but 4+1 drives is more efficient than 3+1. Currently I have three 8TB drives: 1xWD Red and 2xIronwolfs (wolves?) with one running as parity (SHR). No complaints. It does everything I need it to do. The interface is simple and everything "just works" as anticipated. If/when I run out of space I plan on adding another 2x8TB drives, probably more ironwolves.
I wouldn't go bigger than 8TB as they already take DAYS to add to the array.