@lanodan @roboneko @shibao @EdBoatConnoisseur so raid1c3 is you have a pool of disks but every file is stored on at least 3 disks so you can lose 2 disks without losing data.
It's like RAID 6/raidz2 but no math involved and lots of wasted disk space. Btrfs has had support RAID 6 for a few years now but don't use it outside of testing because you have a good likelihood of data corruption still.