GEOM gotcha upgrading from 6.x to 7.x

[Oliver Brandmueller]

Hello,

On Sat, Jun 28, 2008 at 07:49:12AM +1000, Peter Jeremy wrote:
> Yesterday, I planned to try an upgrade from 6.x to 7.x on one of the
> servers at work, on the assumption that I could reasonably easily
> revert to 6.x if things went bad.  My confidence in being able to
> do that was severely shaken when I saw "Upgrading metadata" messages
> for both geom_mirror disks when the 7.x kernel booted.
> 
> Whilst I did not need to revert, some examination of the geom_mirror
> source shows that (as I feared), a 6.x kernel will choke on a 7.x
> geom_mirror.

I didn't try now, but from my experience it should be fairly easy to 
revert: Boot without gmirror from one the disks with the old kernel. 
Have an old world available (CD, not yet installworld'ed) an write 
gmirror label from single user mode with old metadata, add the other 
disk and rebuild (more or less just go the way you go to setup a 
bootable gmirror from an existing system).

You would be in more trouble if you had some kind of real RAID format 
(like a RAID 5 or something) on the disk, but gmirror is basically a set 
of metadata whilst any single disk of the mirror is actually in a 
format, that can be used without gmirror.

I agree, that this is not actually straigt forward (as downgrading isn't 
anyhow), but for the case "I see my 7.x kernel choking when upgrading 
from 6.x to 7.x" it should still be easy enough for an experienced 
admin.


Greetings,
		Oliver


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