Comment # 3 on bug 1174939 from William Brown

So I gave in and tried this.

pyrite# btrfs quota rescan /
ERROR: quota rescan failed: Read-only file system

[33459.328631] BTRFS warning (device vda2): qgroup rescan init failed, qgroup
is not enabled

So it looks like it's not able to to be fixed with transactional server unless
you take steps like:

pyrite# mount -o remount,rw /
pyrite# btrfs quota rescan /
ERROR: quota rescan failed: Invalid argument

[33965.861982] BTRFS info (device vda2): disk space caching is enabled
[33967.386755] BTRFS warning (device vda2): qgroup rescan init failed, qgroup
is not enabled