source: used to work for a storage vendor that was marketing a NAS based on ZFS and got credible threats from Netapp to the point that we sought a partnership with Oracle that included indemnification under Oracles settlement with Netapp.
* https://www.theregister.com/off-prem/2010/09/09/oracle-and-n...
* https://www.computerworld.com/article/1585889/opinion-patent...
NetApp originally sued then-independent Sun in 2007, and Sun counter-sued.
Free/TrueNAS/iXsystems has been offering ZFS-based solutions for many years now, and I haven't heard NetApp going after them:
Maybe he was ... they do that sometimes.
I looked around a little. the C&D from Netapp was in ~July 2010 and the partnership and product with Oracle in the Fall (Around the cease fire) and we continued with that (via the Oracle Partnership) through 2011-2015 when the company ran out of cash and laid us all off.
I was just a lowly support engineer so not privy to all the legal details that the executives were dealing with. I too had to just take them at their word.
ETA: I searched a bit. Here's a link
https://www.enterprisestorageforum.com/networking/netapp-thr...
Maybe threats were enough? I certainly wouldn't want to test it myself.