You should enable several services as follows:
sudo systemctl enable zfs-import-cache.service
sudo systemctl enable zfs-import-scan.service
sudo systemctl enable zfs-mount.service
sudo systemctl enable zfs-share.service
sudo systemctl enable zfs-zed.service (depending on version may be zed.service)
and also:
sudo systemctl enable zfs.target
Reboot and see what happens. Because of different versions and distributions, these may not all exist on you system. Any that do should be enabled.
EDIT1:
To see if these services were properly enabled, execute the following command:
ls -oR /etc/systemd/ |grep zfs
The output should look something like:
drwxr-xr-x 2 root 4096 22.01.2017 17:31 zfs-mount.service.wants/
drwxr-xr-x 2 root 4096 22.01.2017 17:31 zfs-share.service.wants/
drwxr-xr-x 2 root 4096 22.01.2017 17:31 zfs.target.wants/
lrwxrwxrwx 1 root 39 22.01.2017 17:31 zed.service -> /usr/lib/systemd/system/zfs-zed.service
lrwxrwxrwx 1 root 34 22.01.2017 17:32 zfs.target -> /usr/lib/systemd/system/zfs.target
/etc/systemd/system/zfs-mount.service.wants:
lrwxrwxrwx 1 root 48 22.01.2017 17:31 zfs-import-cache.service -> /usr/lib/systemd/system/zfs-import-cache.service
lrwxrwxrwx 1 root 47 22.01.2017 17:31 zfs-import-scan.service -> /usr/lib/systemd/system/zfs-import-scan.service
/etc/systemd/system/zfs-share.service.wants:
lrwxrwxrwx 1 root 41 22.01.2017 17:31 zfs-mount.service -> /usr/lib/systemd/system/zfs-mount.service
/etc/systemd/system/zfs.target.wants:
lrwxrwxrwx 1 root 48 22.01.2017 17:31 zfs-import-cache.service -> /usr/lib/systemd/system/zfs-import-cache.service
lrwxrwxrwx 1 root 47 22.01.2017 17:31 zfs-import-scan.service -> /usr/lib/systemd/system/zfs-import-scan.service
lrwxrwxrwx 1 root 41 22.01.2017 17:31 zfs-mount.service -> /usr/lib/systemd/system/zfs-mount.service
lrwxrwxrwx 1 root 41 22.01.2017 17:31 zfs-share.service -> /usr/lib/systemd/system/zfs-share.service
lrwxrwxrwx 1 root 39 22.01.2017 17:31 zfs-zed.service -> /usr/lib/systemd/system/zfs-zed.service
This will enable you to definitively determine whether the services were enabled even if you forgot the output when you enabled them or if you don't have access to the logs.