I'm not a zumastor developer, but what I understand is that
zumastor/ddsnap has been put on hold while Daniel Phillips was
developing Tux3 (whose development seems to also be on hold).
There was a port of ddsnap to kernel space that was further
extended and seems to still be maintained by Mikulas Patocka
There's also https://github.com/mcpacino/dm-snap-mv
that confirms that Daniel Phillips is still around
Otherwise, one could also consider btrfs or zfs as alternatives.