If your ZFS filesystem is completely full, it can be difficult to free up space. Most people's first impulse is to delete files, but that often fails because ZFS can require free space to record the deletion. A colleague of mine ran into this a few weeks ago. I advised him to try truncating a large file using shell redirection (e.g., "cat /dev/null > my_large_file"), but that didn't work. He was able to free up space using the truncate command, which is available in Solaris 11.
truncate -s 0 my_large_file