Server engineer here.
There's a few different options. Unfortunately there is no one perfect solution, they all have their pro's and cons.
RAID
- Good for performance (not needed for this application)
- Inflexible (need to rebuild entire array if you want to change it which means you need the same amount of free space somewhere else to offload the data while you do it + stuck to buying the same drives / size)
- Not great for power consumption (all drives must spin to access any data)
- Not great wear (all drives wear out at the same rate)
- Not a substitute for backups (it's only redundant on the disk level, doesn't protect you from failures in other hardware or accidental deletions etc)
- Not particularly efficient: you shouldn't use RAID 5 for large drives (4TB+) and even RAID 6 isn't great for larger drives, so then you need to look at RAID 10 (or 0+1) which only gives you half your effective disk space and you still need backups on top of that.
All in all RAID is not a great solution for (cold) data storage. I used to have 8x8TB + 8x4TB in RAID 6 for my data storage but I have moved away from that approach. Great while it works, shit when it inevitably starts to fail due to age.
ZFS
Probably better than RAID for this depending on how you set it up, but can still be a pain to manage. Won't go too deep into this since it's probably too advanced/technical for most people here.
Separate drives (JBOD / mergerfs)
Much better for data storage.
- Only wears out individual disks when you actually use them (particularly important when you also seed from these drives) - so also better for power consumption
- Flexible: you can add and remove drives at will, of any types and sizes (which means you can gradually upgrade and retire old disks), and you only have to offload a single disk worth of data at a time (as opposed to the whole array) + your computer can still treat the whole thing as 1 big disk without having to worry about what goes where (but you have the option if you want that)
- No inherent redundancy, you definitely still need backups
Commercial devices (Synology etc)
- Probably the best option for people who aren't very technical. Offers all of the above options in a user-friendly package with lots of features.
Note on backups
Ideally you want your backups to be in cold storage, and have them sync periodically. Better for disk lifespan (+ you don't want the backup disk to be worn out around the same time as the main disk), better for power consumption, gives you restore ability in case of accidental fuckups, also helps to protect you from freak accidents (power surges, lightning strikes, ...). Having them connected but spun down is good, having them completely disconnected is better (but of course requires manual interaction to sync).
Note on seeding
If you seed, designate 1 disk for it so you don't wear out your entire storage array.
I can go deeper into the subject if you have any questions but I don't want to overload you any more than I already have.