I have a lxd 3.0.1@ubuntu18.04 running docker inside the lxd with btrfs , when quota was enabled on any lxd container in the same storage pool, btrfs will freeze while docker container create/destroy frequently .
disable quota fix this.
I have seen this behavior for a few years now. When we first deployed containers, we used btrfs with quotas and snapshots. After a few weeks of creating/destroying snapshots, we noticed the CPU would hit 100% during snapshot removal. This would essentially freeze all running containers since the disk I/O wait was extremely high (even with SSDs).
The fix: disable btrfs qutoas.