the options i know are:

• unraid (costs moneybut is the simplest to setup and comes with a bunch of extra features, app store etc)
• btrfs (though raid5/6 aren't considered ready for production use)
• mergerfs with snapraid (technically not real time but it's the most flexible)

external usb drives

you have close to 8tb worth of pictures? well i guess we are in r/Datahoarder