Installing without blowing away GRUB/MBR

Mason Loring Bliss mason at
Sat Feb 15 16:52:59 UTC 2014

On Sat, Feb 15, 2014 at 09:18:45AM -0700, Warren Block wrote:

> That article probably does not apply to this situation (or maybe any... I
> added a warning to it last week). A ZFS mirror is probably a better
> solution than ZFS on top of a gmirror.

Yeah, that's the plan.

> Looking back on this thread, I'm confused. The subject says MBR, but then
> the text talks about GPT. If possible, avoid MBR and the "partitions inside
> a partition" mess of EBR or MBR slice/FreeBSD partitions and just use GPT.

Very specifically, here's what I've got. The box in question already
dual-boots Debian and Windows on various disks. Two of the disks are already
GPT and already have Debian Wheezy in various partitions, with GRUB
installed to boot everything. I've got free space at the end of each, and I
want to install FreeBSD there, with most of the space being in a ZFS mirror,
with each half sitting on GELI. I don't want to blow away the existing GRUB -
I want to use it to boot FreeBSD as well as the other systems currently

My current belief is that I can install a stage1/stage2 into a freebsd-boot
partition of some very small size, and that that will be able to use a stage3
off of the ZFS mirror. I also believe that I don't need stage0, as GRUB will
be doing that. I'm not sure about these things.

The other point of uncertainty is if the FreeBSD 10 installer will accomodate
this automatically, just asking me if I want to touch the MBR or not. This
is, for instance, something the Debian installer does.

So, here's one of the disks as it stands:

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  2097kB  1049kB                     bios_grub
 2      2097kB  130MB   128MB                      raid
 3      130MB   450GB   450GB                      raid

There's a third disk that has Windows and some utility space on it. There's
space at the end of the first two that I want to use for FreeBSD, so I'd
theoretically be looking at this mocked-up result:

Number  Start   End     Size    File system  Name  Flags
 1      1049kB  2097kB  1049kB                     bios_grub
 2      2097kB  130MB   128MB                      raid
 3      130MB   450GB   450GB                      raid
 4      450GB   450GB   1MB                        freebsd-boot      
 5      450GB   480GB   30GB                       geli

GRUB in the MBR would pick up an entry for FreeBSD and presumably chainload
the stage1/stage2 from partition 4, unless it can deal with the ZFS mirror
sitting on GELI directly, which would shock me.

Currently the Linux portions form a RAID 1, LUKS sits on that, LVM sits on
that... The FreeBSD side will have GELI at the bottom since ZFS incorporates
the mirroring and volume management functionality, really everything but the
encryption itself. (I'd love it if it did the encryption too. =shakes fist at
Oracle=) I don't know if the freebsd-boot would go on a gmirror or if I'd
just tell things that update it to touch both disks. With GRUB, I do the
latter - update-grub writes to both disks.

My understanding is that this is pretty much what I'd get out of the
installer if I said I wanted encrypted, mirrored ZFS - the only difference is
that I want to preserve the existing GRUB.

I'm taking off for a car appointment soon, and depending on what I read once
I get back I'll either try the install directly on hardware, or simulate it
in a VM first. I'd rather save the time and go straight to hardware if what I
want to do doesn't look too thorny.

Mason Loring Bliss   ((  "In the drowsy dark cave of the mind dreams
mason at     ))  build  their nest  with fragments  dropped  ((   from day's caravan." - Rabindranath Tagore

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