ZFS on Linux large scale deployments: 55 Petabytes at LLNL

http://www.slideshare.net/MatthewAhrens/open-zfs-linuxcon

See slide 3; last slide has a little more detail.

ZFS on illumos: Nexenta claims 1.5 Exabytes under management (across multiple deployments)

http://billroth.ulitzer.com/node/2461630

FWIW, my understanding is that CDDL, as a MPL-derived license, had a patent licensing clause and therefore the patents don't matter as long as it's using that set of source code. So a clean room rewrite might run afoul of patents, but the existing CDDL licensed code is okay. (See CDDL, section 2.1(b), but keep in mind section 2.1(d) where modifications and deleted code are not covered.)