If you’re doing it from scratch, I’d recommend starting with a filesystem that has parity checks and filesystem scrubs built in: eg BTRFS or ZFS.

The benefit of something like BRTFS is that you can always add disks down the line and turn it into a RAID cluster with a couple commands.

I mean, recovery from parity data is how all of this works, this just doesn’t require you to have a controller, use a specific filesystem, have matching sized drives or anything else. Recovery is mostly like any other raid option I’ve ever used.

The only drawback is that the parity data is mostly equivalent in size to the actual data you’re making parity data of, and you need to keep a couple copies of indexes since if you lose the index or the parity data, no recovery for you.

In my case, I didn’t care: I’m using the oldest drives I’ve got as the parity drives, and the newer, larger drives for the data.

If i were doing the build now and not 5 years ago, I might pick a different solution but there’s something to be said for an option that’s dead simple (looking at you, zfs) and likely to be reliable because it’s not doing anything fancy (looking at you, btrfs).

From a usage (not technical) standpoint, the most equivalent commercial/prefabbed solution would probably be something like unraid.