AHCI driver and static device names

[perryh at pluto.rain.com]

CyberLeo Kitsana <cyberleo at cyberleo.net> wrote:

> You cannot combine GPT with glabel (or any other geom class
> that writes data to the first or last 34 sectors of a disk,
> like gmirror) due to layout conflicts.

This is overstated.  Since a GPT ordinarily is intended to be booted
from, and so must be recognized by the BIOS, it must be written
directly on the actual drive -- the "rank 1 provider" in GEOM terms
-- because that is the only way for the GPT metadata to be located
where the BIOS expects to find it (at both the beginning and the end
of the drive).

It is, however, possible to combine GPT with gmirror, gjournal,
etc. by using GPT partitions, rather than drives, as providers
for the other geoms.  For example, create a mirror from ad0p1
and ad2p1 rather than from ad0 and ad2.  Similarly, it "should"
be possible to glabel a GPT partition -- although this seems
unlikely to be useful in practice since GPT provides its own
labelling scheme.