That's not at all what happened. (Disclaimer: I was at Sun at the time and was deposed in the case.) Sun didn't "go after NetApp" -- NetApp tried to buy some StorageTek patents via a third-party intermediary, and when they were rebuffed, they came after ZFS.[1] And, it should be said, NetApp didn't particularly care about Sun -- they cared about the fact that ZFS was open source. NetApp wanted Sun to "close" ZFS or otherwise "restrict its use"[2]. As for the case itself, it was moved back to California (NetApp had initiated it in East Texas, the patent troll capital of the universe) where it became a massive case, and was then slimmed down by order of the magistrate to three patents on the NetApp side and four patents on the Sun countersuit side. At the same time, thanks to a community outpouring of prior art, Sun was able to pursue invalidating the claims of the NetApp patents with the US Patent Office.[3] These efforts were wildly successful, and all three NetApp patents were rejected on all claims. Amazingly, the case wasn't thrown out at that point (though any damages would obviously be very limited), but every turn in the case had gone Sun's way.
Then, Oracle acquired Sun, and for reasons that haven't been disclosed, Oracle and NetApp dismissed their respective cases.[4] While I can't disclose the reasons behind this, I can say that both Oracle and NetApp would have jumped at the chance to cross-license ZFS and WAFL patents in a way that extended only to Oracle and not to CDDL licensees. (That is, prohibited open source ZFS.) Because the CDDL is airtight with respect to patents, such cross-licensing was impossible, and by dismissing their suits (instead of settling), the findings of fact from the trial essentially disappear -- which is enormously to NetApp's advantage. Point is: ZFS actually has about as much patent security as one can find in an open source system, as it has withstood a direct, full-frontal assault by attorneys seeking to find a way around its patent grants.
Then, Oracle acquired Sun, and for reasons that haven't been disclosed, Oracle and NetApp dismissed their respective cases.[4] While I can't disclose the reasons behind this, I can say that both Oracle and NetApp would have jumped at the chance to cross-license ZFS and WAFL patents in a way that extended only to Oracle and not to CDDL licensees. (That is, prohibited open source ZFS.) Because the CDDL is airtight with respect to patents, such cross-licensing was impossible, and by dismissing their suits (instead of settling), the findings of fact from the trial essentially disappear -- which is enormously to NetApp's advantage. Point is: ZFS actually has about as much patent security as one can find in an open source system, as it has withstood a direct, full-frontal assault by attorneys seeking to find a way around its patent grants.
[1] https://web.archive.org/web/20070423001711/http://blogs.sun....
[2] https://web.archive.org/web/20080625023043/http://blogs.sun....
[3] http://www.theregister.co.uk/2008/10/07/sun_gets_netapp_pate...
[4] http://www.theregister.co.uk/2010/09/09/oracle_netapp_zfs_di...