unable to boot to FreeBSD 10.1-RELEASE-p31

[Trond Endrestøl]

On Fri, 18 Mar 2016 15:38-0000, Rao, Uthra R. (GSFC-672.0)[ADNET SYSTEMS...:

> I updated my FreeBSD 10 system to 10.1-RELEASE-p31 and rebooted. The system is not booting. I see the following message on the screen:
> 
> ZFS: i/o error - all block copies unavailable
> ZFS: can't read MOS of pool tank
> gptzfsboot: failed to mount default pool
> 
> Please let me know how I can fix this issue.

Here's a quick laundry list:

Ensure all disks are available and visible to the firmware. Someone 
else on one of the lists made a change to the disk controller, thus 
limiting the number of visible disks. Once that was rectified 
everything was back to normal.

A description of your zpools layout would be nice. Any changes done to 
your zpools during operation prior to reboot, like adding disks only 
visible to the kernel, and not the firmware nor the boot loaders.

Try booting one of the 10.3 snapshots to see if the pools are healthy.

I hope others might chime in with far better suggestions than mine.

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