Insane file system overhead on large volume

[Manny]

Hi there,

I'm not sure if this is intended behavior, but I was a bit stumped
when I formatted a 30TB volume (12x3TB minus 2x3TB for parity in RAID
6) with XFS and noticed that there were only 22 TB left. I just called
mkfs.xfs with default parameters - except for swith and sunit which
match the RAID setup.

Is it normal that I lost 8TB just for the file system? That's almost
30% of the volume. Should I set the block size higher? Or should I
increase the number of allocation groups? Would that make a
difference? Whats the preferred method for handling such large
volumes?

Thanks a lot,
Manny