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Date: Thu, 12 Dec 2013 17:32:52 +0200
From: Andriy Gapon <avg@FreeBSD.org>
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To: "Eugene M. Zheganin" <emz@norma.perm.ru>, freebsd-stable@FreeBSD.org
Subject: Re: zfs i/o error - all block copies unavailable
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on 12/12/2013 15:31 Eugene M. Zheganin said the following:
> =>        34  7814037101  ada1  GPT  (3.6T)

At work we recently had a problem with the 3TB disks on certain systems.
Apparently BIOS silently failed to read offsets >= 2TB.  Probably it just read
from wrong offsets (e.g. modulo 2TB).  So, if any files important for booting
like zfsloader or kernel or mandatory boot configuration files ended up at the
large offsets, then the system just would not boot.
As a precise location of the files on disk is not predictable we had to create a
smaller partition specifically for the root pool.

Not sure if you have the same issue, but this is something to keep in mind.

-- 
Andriy Gapon