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Date: Thu, 20 Mar 2014 11:52:11 -0400
From: Adam McDougall <mcdouga9@egr.msu.edu>
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To: freebsd-stable@freebsd.org
Subject: Re: Can ZFS boot from other than the root of a pool?
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On 03/20/2014 10:30, Karl Denninger wrote:

>>> On Mar 20, 2014 7:13 AM, "Karl Denninger" <karl@denninger.net> wrote:
>>>> For a number of reasons having to do with backup strategy I want to
>>>> mount
>>> a ZFS root from "poolname/root" instead just "poolname."
>>>> That works ok; I can set in /boot/loader.conf:
>>>> vfs.root.mountfrom="zfs:zroot/root"
> It LOOKS to me like this will work too:
> 
> zpool set bootfs tank/bootfs
> 
> ... and in loader.conf (in /boot/loader.conf on tank/bootfs) set the
> root SOMEWHERE ELSE.
> 
> That has certain advantages, particularly if you want a GELI-encrypted
> root.
> 
> I'll play with this a bit.... (the ability to make upgrades much less
> dangerous in that an immediate-revert becomes pretty easy helps too)
> 

You don't need to set vfs.root.mountfrom in recent versions.  This makes
it much easier.  I've been booting from /rpool/ROOT/freebsd for years
(sometimes alternate paths when I want to load another copy of FreeBSD).
 Setting bootfs should do the trick.