correct way to setup gmirror on 7.4?

[Freddie Cash]

On Wed, Apr 27, 2011 at 3:15 PM, Clifton Royston <cliftonr at lava.net> wrote:
>  I don't know; it looks correct to me, but I may be missing something
> as I don't currently use gpart.

gmirror (well, really, any GEOM) doesn't play well with GPT due to the
way they store their metadata.

gmirror doesn't touch the start of the disk, but saves it's metadata
in the last sector of the disk, and creates a new GEOM provider that's
one sector shorter.

GPT stores it's partition table in the first sector of the disk, and
saves a backup copy of it in the last sector of the disk.

Depending on the order you do things, gmirror can overwrite the
secondary GPT table.  Or, if you mirror the disk and then gpart the
mirror, gpt will complain that the secondary table is not in the last
sector of the disk (due to the order that GEOM tastes things as gpt
goes first).

I've tried to document it here.  Let me know if there's anything incorrect.
https://forums.freebsd.org/showthread.php?t=22125


-- 
Freddie Cash
fjwcash at gmail.com