The legibility of different versions of ZFS
I'll put the summary right up at the front: one of the refreshing things that I enjoy about OpenZFS on Linux is how comparatively legible and accessible some aspects of its operation are to me. Well, specifically how comparatively legible starting up ZFS on boot is. Now, there are two sides to that. On one side, the Linux setup to start ZFS is complicated. On the other side, this complexity has always existed in ZFS, it's just that on Solaris (and Illumos/OmniOS), the complexity was deliberately hidden away from you. You were not supposed to have to care about how ZFS started on Solaris because the deep integration of ZFS with the rest of the system should make it just work.
This was fine until the time when it didn't just work. We had some of those at some points, and because we had some of those (and as a general precaution), I wanted to understand the whole process more. When we were running Solaris and then OmniOS, I mostly failed. I never fully understood things like ZFS pool activation and iSCSI or boot time pool activation (also). I'm sure that these things are knowable, and I suspect that they are knowable even for people who aren't Illumos ZFS kernel developers, but I was never able to navigate through everything while we were still running OmniOS.
Given how we overlooked
it's quite possible that part of what is going on is that I'm more
familiar with Linux boot arcana than I am with Illumos boot arcana.
I certainly like systemd much more than SMF,
which left me more interested in learning systemd things than in
learning SMF ones. And OpenZFS on Linux has no more documentation
on the ZFS boot process in Linux than Illumos had for its ZFS boot
process the last time I looked, so you're at the mercy of third
party documentation like the Arch wiki. But for
whatever reasons, I've been more successful at figuring out the
Linux ZFS boot process than I ever was with the OmniOS one.
(Illumos also comes pre-set to have all of the ZFS things work while OpenZFS on Linux can leave you to configure things yourself, which is not exactly the greatest experience.)
I do wish that these things were documented (for Illumos and OpenZFS both). They don't have to be officially supported as 'how this will be for all time', but just knowing how things are supposed to work can be a great help when you run into problems. And beyond that, it's good to know more about how your systems operate under the surface. In the end there is no magic, only things that you don't know.