Hello
The current ZFS version provided by openmediavault-zfs and zfsutils-linux is 0.7.6.
This version is not compatible with the Linux kernel version 4.16 and fails to build.
ZFS will be unusable until ZoL 0.7.8 or above is released in the Debian repository.
The release of 0.7.8 is still pending.
Sources:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=897568
https://tracker.debian.org/pkg/zfs-linux
https://github.com/zfsonlinux/zfs/issues/7179
Greetings
Vincent