It is worth noting that the GPL2-CDDL license incompatibility is still a theoretical legal issue, and that there are differing learned opinions with respect to the confluence of the CDDL, GPL2, and ZFS. For instance, Eben Moglen, co-author of the GPL3, has indicated that incompatibility is not an issue[0]. Many Sun employees have also disagreed that Sun's intent was to make the CDDL incompatible with the GPL2.

[0] https://www.softwarefreedom.org/resources/2016/linux-kernel-...