Yet another knock-off of Lustre. Lustre is not perfect, and I'm not suggesting it has a place in the mainline kernel, but it sounds like neither does BTRFS.

When you get to large scale (multi-petabyte) filesystems there are not many options, it's GPFS, Lustre, or roll your own. Lustre development has been indirectly sponsored by the DoE for a long time now. And if Lustre didn't exist IBM would charge even more for GPFS. But at least Lustre is free. But it's not a walk in the park to use.