IIRC, OpenZFS is the ZFS in Illumos. It's just not the ZFS in Oracle's Solaris.
OpenZFS was created as a way to combine development of all the versions of ZFS across Linux, FreeBSD, Illumos, and others. If you're using a (fairly) recent Illumos, you're using OpenZFS.
Disclaimer: Not an OpenZFS developer; just a happy user.
Not exactly, take a look at the list of supported platforms in the releases notes of TFA -- OpenZFS 2 as a unified codebase is currently only ported to Linux and FreeBSD. Illumos is still using the older ZFS code with fewer features.
The whole history is pretty convoluted, since I'm fairly certain "OpenZFS" has been used to refer to several completely different source trees, with the Linux, FreeBSD, OS X, NetBSD, and Windows ports of ZFS all being separate forks off of the ZFS code from early OpenSolaris releases.
Despite the licensing drama and general distaste most distros and Linus have/had for ZoL, the Linux port had sort of become the de facto "standard" for ZFS development, with more work being done on that version of the source tree.
I only followed the "drama" from a distance, don't use ZFS or FreeBSD very frequently, but I know there was an internal discussion a while back within FreeBSD where they decided to pull commits directly from the ZoL tree instead of Illumos, because that tree was more active, and otherwise they had to wait on any improvements from Linux to be merged to the upstream Illumos tree.
The elephant in the room was the lack of activity in Illumos and the gradual decline of industry sponsors and development over the years. I don't know what the current state is, and I'm not saying Illumos is "dead", but it's definitely a shadow of its prime back when Joyent and a lot of companies were really pushing and developing on it. Several big names dropped out of Illumos development, including some NAS companies IIRC.
Anyway, OpenZFS 2, AFAIK, is essentially a rebranding of ZFS on Linux, but with CI/CD pipelines testing every commit against FreeBSD as well, basically unifying the work for Linux + FreeBSD.
The other versions (Mac, NetBSD, Windows, others?) still use separate forks AFAIK.
> Despite the licensing drama and general distaste most distros and Linus have/had for ZoL, the Linux port had sort of become the de facto "standard" for ZFS development, with more work being done on that version of the source tree.
This actually happened because of one feature: ZFS encryption. That feature was developed for ZoL first, and had to be ported to other platforms. The developer of the feature for ZoL did not want to write it for Illumos first and port it to Linux later.
The consequence of that is that the Linux port got its first significant feature the others didn't have, and there was no real assistance to bring it into the other platforms quickly. That led to a bit of a political mess where the fallout was the "new" OpenZFS codebase where Linux and FreeBSD are maintained in one tree.
Source: I observed the whole thing while working at the place that wrote ZFS encryption for ZoL.
It's very convoluted, and I probably got some details wrong, but that's the gist of what GP was probably thinking about.
Not sure what the Illumos guys ended up doing in response, either. My memory from browsing their mailing lists was they were pretty surprised by FreeBSD's decision, and didn't seem particularly happy about it, since Illumos/OpenSolaris is the "proper home" of ZFS, but...
OpenZFS was created as a way to combine development of all the versions of ZFS across Linux, FreeBSD, Illumos, and others. If you're using a (fairly) recent Illumos, you're using OpenZFS.
Disclaimer: Not an OpenZFS developer; just a happy user.