Gmirror on a partition of a slice

[n j]

On 9/21/07, Ivan Voras <ivoras at freebsd.org> wrote:

> > The logic behind this is probably that if you already partition or
> > label the underlying consumers, you must not do the same with the
> > provided mirror, i.e. you can't really treat the provided mirror as an
> > entirely fresh new disk. As I said, this is maybe obvious to someone,
> > but for me it was new.

> Actually, you *can* do it if you really want to, because every GEOM
> provider is a "whole disk" to the system, it's just that usually it's
> not what you want.

That is what I thought at first, but I spent a couple of days trying
to boot off such a geom "disk" and had absolutely no success until I
skipped the two steps Pawel pointed out. Actually, I'm beginning to
think that OS has to read the boot code from an actual (physical) disk
partition like da0s1a/da1s1a. In case you skip fdisk&bsdlabel on the
gmirrored partition, gm0 remains the exact copy of the actual boot
partition, da0s1a, and OS boots. By fdisk'ing and bsdlabel'ing  the
newly created disk, gm0, my understanding is that you actually change
the underlying (boot) partition, da0s1a, and mess it up enough to make
the system unbootable.

The above interpretation, OTOH, might be completely wrong. My
understanding of the boot process is very vague and you might be
right. I'm not saying it's not possible, I'm just saying that I tried
it and it didn't work, no matter how hard I try. If you care to
describe the necessary steps on how to do it, I'll try again.

Regards,
-- 
Nino