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From: Richard Todd <rmtodd@ichotolot.servalan.com>
Date: Fri, 25 Jan 2008 23:48:28 -0600
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	(Joe Peterson's message of "Fri, 25 Jan 2008 18:17:24 -0700")
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Subject: Re: "ad0: TIMEOUT - WRITE_DMA" type errors with 7.0-RC1
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Joe Peterson <joe@skyrush.com> writes:

> Glad you got it back!  Yes, when I was first playing with ZFS, I noticed
> that booting between single and multi user mode could make the pools
> "invisible".  Import seemed to bring them back...

Yeah.  ZFS pools record the hostid of the system that accessed them last.
When you boot in single-user mode, /etc/rc.d/hostid doesn't get run,
so the hostid is zero, which doesn't match the hostid in the pool, so the
pool doesn't show up without an import.  Workaround: always make sure you
run /etc/rc.d/hostid start in single-user before doing any ZFS tinkering.