ZFS Panic after freebsd-update

[Andriy Gapon]

on 01/07/2013 21:50 Jeremy Chadwick said the following:
> The issue is that ZFS on FreeBSD is still young compared to other
> filesystems (specifically UFS).

That's a fact.

> Nothing is perfect, but FFS/UFS tends
> to have a significantly larger number of bugs worked out of it to the
> point where people can use it without losing sleep (barring the SUJ
> stuff, don't get me started).

That's subjective.

> I have the same concerns over other
> things, like ext2fs and fusefs for that matter -- but this thread is
> about a ZFS-related crash, and that's why I'm "over-focused" on it.

I have an impression that you seem to state your (negative) opinion of ZFS in
every other thread about ZFS problems.

> A heterogeneous (UFS+ZFS) setup, rather than homogeneous (ZFS-only),
> results in a system where an admin can upgrade + boot into single-user
> and perform some tasks to test/troubleshoot; if the ZFS layer is
> broken, it doesn't mean an essentially useless box.  That isn't FUD,
> that's just the stage we're at right now.  I'm aware lots of people have
> working ZFS-exclusive setups; like I said, "works great until it
> doesn't".

Yeah, a heterogeneous setup can have its benefits, but it can have its drawbacks
too.  This is true for heterogeneous vs monoculture in general.
But the sword cuts both ways: what if something is broken in "UFS layer" or god
forbid in VFS layer and you have only UFS?
Besides, without mentioning specific classes of problems "ZFS layer is broken"
is too vague.

> So, how do you kernel guys debug a problem in this environment:
> 
> - ZFS-only
> - Running -RELEASE (i.e. no source, thus a kernel cannot be rebuilt
>   with added debugging features, etc.)
> - No swap configured
> - No serial console

I use boot environments and boot to a previous / known-good environment if I hit
a loader bug, a kernel bug or a major userland problem in a new environment.
I also use a mirrored setup and keep two copies of earlier boot chains.
I am also not shy of live media in the case everything else fails.

Now I wonder how you deal with the same kind of UFS-only environment.
-- 
Andriy Gapon