How many drive bays do I actually need?

Reviewers and community threads suggest a 2-bay unit is plenty for photo/file backup and light streaming with one drive of redundancy, while a 4-bay gives room for RAID 5/6 and a media library that grows. Verified-purchase reviewers of 2-bay units like the DS223 and DXP2800 report they comfortably handle backups and basic Plex/Jellyfin, whereas creators moving 4K footage gravitate to 4-bay 10GbE models.