btrfs官方文档，对scrub+raid56的评价是mostly ok https://btrfs.readthedocs.io/en/latest/btrfs-man5.html#raid56-status-and-recommended-practices
When scrub is started on a RAID56 filesystem, it’s started on all devices that degrade the performance. The workaround is to start it on each device separately. Due to that the device stats may not match the actual state and some errors might get reported multiple times.