

If you’ve got two 3.5" bays, you could do a RAID 1 (or a mirror in ZFS terms) with them both. This works very nicely with a small SSD for booting. My TrueNAS server has a 120 GB SSD in the M.2 slot that TrueNAS is installed on, then I have an array of spinning disks that forms the main storage array.
If you are planning any sort of play environment that you might want to keep (like a Pixelfed instance) I’d strongly recommend RAID just for availability in the event of a drive failure. But more than that, backups. They are of number one importance. Before you turn up anything of any importance, figure out a backup strategy.
It’s most useful for something like /home so you have a full backup of your home directories without having to worry if some app has dumped its settings on a folder you don’t have marked for backup. But also backing up / is useful because it gives you an easy recovery in the event of say disk failure. Just restore the entire system from a backup.