Recently it was discovered that the RAID 5/6 implementation in Btrfs is broken, due to the fact that can miscalculate parity (which is rather important in RAID 5 and RAID 6).
So what to do with an existing setup that’s running native Btfs RAID 5/6?
Well, fortunately, this issue doesn’t affect non-parity based RAID levels such as 1 and 0 (and combinations thereof) and it also doesn’t affect a Btrfs filesystem that’s sitting on top of a standard Linux Software RAID (md) device.
So if down-time isn’t a problem, we could re-create the RAID 5/6 array using md and put Btrfs back on top and restore our data… or, thanks to Btrfs itself, we can live migrate it to RAID 10!