[Someone]

The on-disk format is available (http://www.giis.co.in/Zfs_ondiskformat.pdf)

That PDF says ”Unless otherwise licensed, use of this software is authorized pursuant to the terms of the license found at: http://developers.sun.com/berkeley_license.html”*. That link is broken, but it seems that’s Berkeley license (whatever that means for a specification, and for which variant?)

According to http://open-zfs.org/wiki/Developer_resources, its outdated, but still useful.

I think I would use that, rather than spend months diffing disk images.