unable to boot to FreeBSD 10.1-RELEASE-p31

[pathiaki2]

On 03/18/2016 11:48, Trond Endrestøl wrote:
> 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.
>
After you follow through on all the above, if it doesn't resolve it.

Do a man gptzfsboot and follow the examples.  You will probably want to 
stamp a new bootstrap on the boot drive partition.  (This is only if you 
used GPT and the BOOT disk is ZFS - seems to be)

Since you probably have the media on a USB or DVD, boot from it and get 
into a shell and re-stamp the bootstrap on the correct disk.

gpart show <RET>

will show you the partition table.  Chances are, partition 1 is the one 
you want to stamp and should say freebsd-boot:

  gpart show

=>        34  5860533101  ada0  GPT  (2.7T)
           34           6       - free -  (3.0K)
           40        1024    1  freebsd-boot  (512K)    <------SEE THIS?
         1064     4194304    2  freebsd-swap  (2.0G)
      4195368        3032       - free -  (1.5M)
      4198400  5856333824    3  freebsd-zfs  (2.7T)
   5860532224         911       - free -  (456K)