It is actually more like RAID-1E which is supported by some hardware RAID HBA. The difference is that RAID-1E is usually using strict sequential block placement algorithm and assumes disks of equal size, while btrfs raid10 is more flexible in selecting where next mirror pair is allocated.
s/flexible/random/In sense, with btrfs, you can't really choose where the blocks are allocated, that's not really the definition of "flexible"?
