Recently the cluster upgrade to 4.13 and since than the containers cannot be deleted. The system gives an error.
$ lxc delete test-1 --project development
Error: Error deleting storage volume: Failed to run: zfs destroy -r local/containers/development_test-1: cannot destroy 'local/containers/development_test-1: dataset is busy
Like earlier try to see if there is lxcfs process still running. After killing that process it still shows the same error so checked again and got following:
$ sudo grep development_test-1 /proc/*/mounts
/proc/193234/mounts:local/containers/development_test-1 /var/snap/lxd/common/lxd/storage-pools/local/containers/development_test-1 zfs rw,xattr,posixacl 0 0
/proc/219880/mounts:local/containers/development_test-1 /var/snap/lxd/common/lxd/storage-pools/local/containers/development_test-1 zfs rw,xattr,posixacl 0 0
/proc/236080/mounts:local/containers/development_test-1 /var/snap/lxd/common/lxd/storage-pools/local/containers/development_test-1 zfs rw,xattr,posixacl 0 0
/proc/329809/mounts:local/containers/development_test-1 /var/snap/lxd/common/lxd/storage-pools/local/containers/development_test-1 zfs rw,xattr,posixacl 0 0
$ ps aux | grep 219880
root 219880 0.0 0.0 1306984 15356 ? Ss Mar21 0:00 [lxc monitor] /var/snap/lxd/common/lxd/containers development_dev-1
ubuntu 2975502 0.0 0.0 6432 728 pts/0 S+ 03:30 0:00 grep --color=auto 219880
$ ps aux | grep 329809
root 329809 0.0 0.0 1233252 15336 ? Ss Mar21 0:00 [lxc monitor] /var/snap/lxd/common/lxd/containers database-1
ubuntu 2975582 0.0 0.0 6432 736 pts/0 S+ 03:30 0:00 grep --color=auto 329809
Looks like some bug in the way the database and zfs proc mounts were handled during upgrades.