gmirror per partition. Was: Re: gmirror gm0 destroyed on shutdown; GPT corrupt

On Thu, Jun 25, 2009 at 09:41:13AM -0700, Marcel Moolenaar wrote:
> 
> On Jun 25, 2009, at 4:02 AM, Anton Shterenlikht wrote:
> > dev_taste(DEV,mirror/gm0)
> > g_part_taste(PART,mirror/gm0)
> >
> > GEOM: mirror/gm0: the secondary GPT table is corrupt or invalid.
> > GEOM: mirror/gm0: using the primary only -- recovery suggested.
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> You created the mirror after the GPT, which means you destroyed
> the GPT backup header. gmirror uses the last sector on the disk
> for metadata and that by itself is a cause for various problems.
> 
> It's better to use gmirror per partition.

Like this?

# gmirror label -vb round-robin root /dev/da0p2
gmirror: Can't store metadata on /dev/da0p2: Operation not permitted.
#

I've read some boot disk gmirror examples, e.g.

http://people.freebsd.org/~rse/mirror

however, all examples I've seen are for i386, talking about MBR, fdisk
and bsdlabel, so these are not directly applicable to ia64.

Application of gvinum for boot disk on ia64 is not clear either.
It seems gvinum section of the handbook, 21.9, is also based on i386.

Please advise

many thanks
anton

-- 
Anton Shterenlikht
Room 2.6, Queen's Building
Mech Eng Dept
Bristol University
University Walk, Bristol BS8 1TR, UK
Tel: +44 (0)117 928 8233 
Fax: +44 (0)117 929 4423