sysinstall vs gmirror

[perryh at pluto.rain.com]

Adam Vande More <amvandemore at gmail.com> wrote:

> On Sun, Sep 12, 2010 at 11:14 PM, <perryh at pluto.rain.com> wrote:
> > The part I don't know how to do is partitioning gm0 by hand.
> > (I suppose it would require some sort of arcane incantations
> > involving bsdlabel.)  For all its limitations, sysinstall
> > seems at least to know how to translate a reasonably human-
> > readable representation of the desired slice and partition
> > layout into the necessary fdisk and bsdlabel commands.
>
> I don't know of any exact howto, but the general principles are
> laid out here:
>
> http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/Mirror

I finally had time to (try to) read through that, and I'm having
trouble locating a description of how to partition a gmirror.
(The page seems oriented almost entirely to ZFS and gpart, the
only mention of gmirror being in connection with swap.)  I'm quite
sure I don't want to attempt ZFS on a machine with only 512MB, and
I'm not at all sure that a BIOS of this age would understand gpart.

> It shows how to load geom modules from usb stick

I had already figured out that part :)

  Fixit# ln -s /dist/boot/kernel /boot
  Fixit# gmirror load

which is all I think I need until I get the mirror partitioned.

> Next fdisk/gpart accordingly (don't forget to make it bootable).

This is where I get stuck.  I've partitioned the physical drives
using sysinstall, but how do I go about partitioning gm0?

> If your setup if GPT compatible, I recommend using it.

How do I find out whether this setup is GPT compatible?

> IMO, it's significantly more straightforward than the old
> mbr style.

I sure did not get that impression from reading gpart(8) :(

For starters there seem to be at least 6 kernel options, of
which I guess I may need 3: GEOM_PART_BSD, GEOM_PART_GPT, and
GEOM_PART_MBR; there's apparently no "edit" function; and one
has to puzzle out what is meant by a "protective MBR" as part
of understanding how to make a GPT partition bootable.