How many bays do I actually need in a home NAS?

For most households doing photo backup, document storage, and light media streaming, a 2-bay NAS in RAID 1 is sufficient and cheapest to populate with drives. Specialist communities like r/DataHoarder and r/synology consistently recommend a 4-bay unit if you plan to run RAID 5/SHR for better usable capacity, want room to grow, or intend to host Plex/Jellyfin with a large library. Reviewers across r/UgreenNASync also note 4-bay units typically come with stronger CPUs and more RAM, which matters for apps and VMs.