I recommend setting up a NAS separate from the rest of your setup.
First, remember that RAID is not a backup. RAID is used because it allows you to recover from single-drive failures without bringing the whole server down and restoring a backup. RAID does not stop you from accidentally destroying all the data on your NAS by deleting /, re-initializing the array, breaking more than one drive, etc etc.
With that in mind, if you plan to store important data on your NAS, I recommend backing up the entire thing at least once a week. There’s a lot of options: Backblaze, rsync.net, 12tb drive from Aliexpress, tape drive from the dumpster behind the Fishers office…
Whatever you pick, make sure you test your backups to make sure they actually work. There’s nothing worse than finding out your backups don’t exist when you’ve already lost your data.
NAS options:
Prebuilt:
Synology NAS devices
QNAP NAS devices
DIY file server OS options:
TrueNAS
Awesome free option with a ton of features. Can be difficult to set up.
UnRAID
More user friendly. Costs money.
Controllers
https://www.servethehome.com/anatomy-hardware-raid-controller/ https://www.servethehome.com/sas-sata-cables-guide-sff8087-8088-8470-8482-8484-single-device-connectors/ Two types of controller: hardware RAID and HBA (host bus adapter). For a small NAS, you probably want ZFS, which means a plain HBA card.