Thanks for the answer. I had already tried " btrfs balance start -musage=75 -dusage=75 /mnt It only reallocated 3 blocks. But after I had moved some data, I ran it with 90, and it realocated a lot more. I have a new balance running, and this time it seems to be doing its job. At least data is distributed more evenly across disks. Its not done yet, but its looking fine.
