[arch-general] can't balance full btrfs raid6 filesystem

[Jameson Pugh]

I have a raid6 btrfs filesystem which I filled up, and added a disk to:

 > sudo btrfs fi show /dev/sdb
Label: 'raid'  uuid: 96c75e11-ab60-44b6-a450-4cd2831f86f0
        Total devices 5 FS bytes used 917.77GiB
        devid    1 size 465.76GiB used 465.76GiB path /dev/sdb
        devid    2 size 465.76GiB used 465.76GiB path /dev/sdc
        devid    3 size 465.76GiB used 465.76GiB path /dev/sdd
        devid    4 size 931.51GiB used 465.76GiB path /dev/sde
        devid    5 size 1.82TiB used 0.00B path /dev/sdf

Despite having removed files, and added the new device, I still can't 
balance the filesystem:

 > sudo btrfs balance start /mnt/raid
ERROR: error during balancing '/mnt/raid': No space left on device
There may be more info in syslog - try dmesg | tail

Adding -dusage doesn't help:

 > sudo btrfs balance start -dusage=4 /mnt/raid
Done, had to relocate 0 out of 471 chunks
 > sudo btrfs balance start -dusage=5 /mnt/raid
ERROR: error during balancing '/mnt/raid': No space left on device
There may be more info in syslog - try dmesg | tail

Neither dmesg nor journalctl have anything useful. Am I doomed to 
rebuild the filesystem?

I'm actually at the point, now, where I'm considering ZFS  to avoid the 
issues btrfs has with running out of space, free space reporting, and 
cache disks. I really don't want to move to something that isn't GPL 
compatible, but this is getting quite frustrating.

Thanks,
Jameson