unable to boot a healthy zfs pool: all block copies unavailable

[Michael B. Eichorn]

On Fri, 2015-11-06 at 00:29 +0500, Eugene M. Zheganin wrote:
> Hi.
> 
> Today one of my zfs pool disks dies, I was unable to change it on the
> fly (video board was blocking it) so I powered off, changed disk (not
> in
> root pool) and all of a sudden I realized that i cannot boot:
> 
> ZFS: i/o error - all block copies unavailable
> ZFS: can't read MOS of pool zroot
> gptzfsboot: failed to mount default pool zroot
> 
> It was first reboot since October, 16th, when I installed recent 
> -STABLE
> and upgraded zpool. I was pretty confident that I've installed loaders,
> but I tried to reinstall them - no luck. Then I built today's STABLE
> and
> installed loaders from it - same issue. I've even tried to install less
> recent loaders from a server nearby - same issue.
> 
> Two years ago I have encountered similar (if not identical) issue:
> https://lists.freebsd.org/pipermail/freebsd-stable/2013-December/076317
> .html
> The main difference was it was i386. Now I have an amd64 machine. I
> even
> updated it's BIOS, and I still cannot boot. Zpool is fine: I'm writing
> this message from this exact machine, however, I had to boot it from
> today -STABLE from an USB stick.
> 
> I've read about the zfsboottest utility and tried it on my unbootable
> pool - after the bried info about it (traated as healthy) it said "OK".
> I guess no errors were encountered.
> 
> So... what can I do to restore the ability to boot from my root pool ?
> 
> Thanks.
> Eugene

I had something similar happen to me in the last month with a the
installer zfs setup. Unfortunately it was a critical system so I didn't
have time for diagnostics. My pants-on-fire solution was that since the
pool was a mirror, swap a disk out with my spare, reinstall, and
send/receive the data back. Not pretty, but it was my personal
mail/file/web/everything-not-on-the-firewall server.

The pool was accessible from the installer shell and on import to the
fresh system, it just wouldn't boot.

Also in my case it was RELEASE not STABLE, and yes it was consumer grade
hardware.

TLDR: Not just you. Reinstall?
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