ZFS root mount regression

[Garrett Wollman]

<<On Sun, 21 Jul 2019 17:41:59 -0400, Alexander Motin <mav at FreeBSD.org> said:

> I am not sure how the original description leads to conclusion that
> problem is related to parallel mounting.  From my point of view it
> sounds like a problem that root pool mounting happens based on name, not
> pool GUID that needs to be passed from the loader.  We have seen problem
> like that ourselves too when boot pool names collide.  So I doubt it is
> a new problem, just nobody got to fixing it yet.

This seems plausible, except that something clearly did change to
result in these servers finding the correct root pool under 11.2 and
finding the wrong one under 11.3.  Can't say what it might be; there's
nothing in UPDATING that would imply a change.

(I've also seen some evidence that the parallel mounting is
problematic and I'll have to figure out how to disable that.)

-GAWollman