ZFS i/o error on boot unable to start system

[James B. Byrne]

I have reported this on the forums as well.

FreeBSD-12.1p2
raidz2 on 4x8TB HDD (reds)
root on zfs

We did a hot restart of this host this morning and received the following on
the console:

ZFS: i/o error - all block copies unavailable
ZFS: failed to read pool zroot directory object
qptzfsboot: failed to mount default pool zroot

FreeBSD/x86 boot
ZFS: i/o error - all block copies unavailable
ZFS: can't fild dataset 0
Default: zroot/<0x0>
boot:

What has happened?  How do I get this system back up and online?

My first thought is that in modifying rc.conf to change some ip4 address
assignments that I may have done something else inadvertently which has caused
this.  I cannot think of any other changes made since the system was last
restarted a noon yesterday.

​This is an urgent matter.  Any help is gratefully welcomed.

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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
Harte & Lyne Limited          http://www.harte-lyne.ca
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Hamilton, Ontario             fax: +1 905 561 0757
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