I use an external RAID enclosure set up on RAID10, with 4x 3TB drives, giving me 6TB of redundant storage. In addition to this I backup everything in the cloud periodically, giving me protection in case anything happens to my RAID enclosure (fire, theft, etc).
The RAID enclosure is always connected to my computer, and is part of my library in darktable, so I always have access to my full archive of images. Sometimes I will take photos from my most recent trip/outing/session and store them on my internal SSD to edit. They remain there, un-backed-up, for a week or so while doing initial culling and editing, before transferring to the RAID setup and backing up in the cloud. Admittedly, this subjects me to some risk should anything happen to my SSD during that week or so, but that’s a risk I personally am OK with (if I were a professional and had images for clients than I most definitely would send them straight to a redundant setup and backup in the cloud at first possible opportunity).
Here is a great article further explaining the different possible RAID setups
Additionally, it is worth noting that certain RAID types (5 and 6) essentially have a limitation on how much capacity they can protect. This is due to the capacity of the individual drives used, and the URE rate of the modern HDDs. See here for further reading: