Mounting from ufs:/dev/mirror/gm0s1a failed with error 19

[Warren Block]

On Sat, 24 Oct 2015, Dino Vliet via freebsd-questions wrote:

> Dear FreeBSD userlist,2 or 3 years ago I tried to upgrade to freebsd 9.1 through source and as a consequence my gmirrorhas been broken because I ended up with a broken mirror and don't know how to fix it.

It has been running that way for 2 or 3 years?

> Mounting from ufs:/dev/mirror/gm0s1a failed with error 19.
> Loader variables:
>  vfs.root.mountfrom=ufs:/dev/mirror/gm0s1a
>  vfs.root.mountfrom.options=rw
>
> Manual root filesystem specification:
>
>  <fstype>:<device> [options]
>      Mount <device> using filesystem <fstype>
>      and with the specified (optional) option list.
>
>    eg. ufs:/dev/da0s1a
>        zfs:tank
>        cd9660:/dev/acd0 ro
>          (which is equivalent to: mount -t cd9660 -o ro /dev/acd0 /)
>
>  ?               List valid disk boot devices
>  .               Yield 1 second (for background tasks)
>  <empty line>    Abort manual input
>
> I found this on internet:
> gmirror broken after upgrade | The FreeBSD Forums
>
> And at the loader prompt I did this:
>
> set kern.geom.part.check_integrity=0
> boot
>
> And was able to boot but where I'm stuck is that according to that link I should redo the mirror according to this 18.3. RAID1 - Mirroring but how do I proceed exactly if I don't want to loose my data?
>
> So where do I start exactly?

First, make a full backup.  Test it.  Do not skip this step.

Then, create a new mirror on a new drive (or two drives) as shown in the 
Handbook.  Give the new mirror a different name, do not reuse the old 
name.

Use dump/restore to copy the data from the old drive onto the new 
mirror.  Adjust /etc/fstab on the new mirror to boot from the new label 
or device name.

Shut down.  Remove the old drive, putting it someplace safe to act as 
another backup.

Boot from the new mirror.

This is what the Handbook procedure shows.  If you are concerned about 
the procedure, test it on a non-critical machine first.