Of the RAID 0/1/5/6/1+0 levels supported natively by the Btrfs file-system, it's been the RAID 5 and RAID 6 implementations that have been deemed experimental and not yet production ready. Fortunately, that may soon be changing with some fresh Btrfs tool patches...
November 17, 2014
Btrfs RAID Support For RAID 5/6 Is Improving
Read more at Phoronix