Comment # 8 on bug 1063638 from Aaron Williams

I was hit by this recently and I killed the rebalancing in the middle because
my laptop slowed to a crawl (and I couldn't afford to wait). Unfortunately this
left BTRFS in a state where I can only mount it read-only. I'm still trying to
repair it by rebuilding the extent and csum trees but it is taking forever (16
hours on a SSD with 100G root volume).  After forcing a reboot (power button
because the system was so unresponsive) I can no longer mount the root
filesysten read/write and btrfs check --repair crashed afterwards.

As far as I'm concerned, due to this bug, BTRFS is nowhere near ready for prime
time. I should never have accepted the default choice and should have just used
XFS. The fact that it cannot recover from an interrupted rebalancing operation
is of extremely grave concern.