ZFS: i/o error - all block copies unavailable

Matthew Seaman matthew at FreeBSD.org
Mon Feb 22 17:58:35 UTC 2016

On 2016/02/22 17:41, Dan Langille wrote:
> I have a FreeBSD 10.2 (with freebsd-update applied) system at home which cannot boot. The message is:
> ZFS: i/o error - all block copies unavailable
> ZFS: can't read MOS of pool system
> gptzfsboot: failed to mount default pool system

This always used to indicate problems with /boot/zfs/zpool.cache being
inconsistent.  However, my understanding is that ZFS should be able to
cope with an inonsistent zpool.cache nowadays.

The trick there was to boot from some other media, export the pool and
then import it again.

> The screen shot is https://twitter.com/DLangille/status/701611716614946816
> The zpool name is 'system'.
> I booted the box via mfsBSD thumb drive, and was able to import the zpool: https://gist.github.com/dlangille/6da065e309301196b9cd <https://gist.github.com/dlangille/6da065e309301196b9cd>

... which means all the zpool.cache stuff above isn't going to help.

> I have also run: "gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 XXX" against each drive. I did with the the files
> provided with mfsBSD and with the files from my local 10.2 system.  Neither solution changed the booting problem.
> Ideas?  Suggestions?

Is this mirrored or RAIDZx?  If it's mirrored, you might be able to:

  - split your existing zpool (leaves it without redundancy)
  - on the half of your drives removed from the existing zpool,
    create a new zpool (again, without redundancy)
  - do a zfs send | zfs receive to copy all your data into the
    new zpool
  - boot from the new zpool
  - deconfigure the old zpool, and add the drives to the new zpool
    to make it fully redundant again
  - wait for lots of resilvering to complete

However, this really only works if the pool is mirrored throughout.
RAIDZ users will be out of luck.



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