Create a dedicated ZFS docker pool with deduplication disabled in case of dedup enabled on your system:
zfs create -o mountpoint=/var/lib/docker -o dedup=off rpool/docker
Sometimes, you don't want ZFS for docker storage. ZFS can be sadly quite painful with Docker in Docker and similar scenarios. It might be best to avoid the problem by creating a volume in your ZFS pool, formatting that volume to ext4, and having docker use "overlay2" on top of that, instead of "zfs".
zfs create -s -V 30G rpool/docker
mkfs.ext4 /dev/zvol/rpool/docker
