ZFS i/o error on boot unable to start system

mike tancsa mike at sentex.net
Mon Mar 2 15:31:01 UTC 2020

On 2/28/2020 8:51 AM, James B. Byrne via freebsd-questions wrote:
> 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
> What has happened?  How do I get this system back up and online?

Could be a number of things. e.g. you might have only installed the boot
block on one disk and thats no longer in the boot order.  Your BIOS
might have changed from legacy to EFI only and all of a sudden you
cannot boot the disks as you dont have the right boot loader. (This
happened to me once). 

As others have said, try booting off a usb stick and see if the pool is
OK and then take a look at the parts that are involved in the boot
process as outlined by trond.endrestol at ximalas.info


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