Convert MBR Partitions to GPT

Thomas D. Dean tomdean at
Mon Sep 2 13:54:46 UTC 2019

On 9/2/19 5:11 AM, Polytropon wrote:
> On Mon, 2 Sep 2019 05:04:52 -0700, Thomas D. Dean wrote:
>> On 9/2/19 4:39 AM, Polytropon wrote:
>>> On Sun, 1 Sep 2019 19:47:33 -0700, Thomas D. Dean wrote:
>>>> I have 5 disk drives, with two (same) OS's.  Actually, two drives have
>>>> Windows 7 and its secondary plex.  From an earlier post:
>>>> sata6g_1  HD0 SSD    ubuntu 18.04
>>>> sata6g_2  HD1 WD5000 Ubuntu 18.04
>>>> sata3g_3  HD2 WD5000 windows 7 - not used
>>>> sata3g_4  HD3 WD5000 backup
>>>> sata3g_5  HD4 WD5000 windows 7 secondary plex- not used
>>>> sata3g_6  DVD DRW-24B3LT
>>>> sata6g_E1 (empty)
>>>> sata6g_E2 (empty)
>>>> I plan to keep the SSD Ubuntu install until I can get FreeBSD up and
>>>> running the way I want.
>>>> So, for now, I want to install FreeBSD on sata3g_5 HD4.
>>>> My motherboard, ASUS P9X79 PRO has support for UEFI boot.
>>>> Is it worth the effort to change everything to GPT, or, should I just
>>>> use GPT on the FreeBSD disk?  I am leaning toward the later, but, ...
>>>> I think the future has a SSD for FreeBSD.
>>> Don't confuse UEFI and GPT. :-)
>>> YOu can use both GPT and MBR (not on the same disk, of course,
>>> but on different disks). Choosing MBR is suggested today only
>>> for the few cases where it's absolutely needed. Use GPT if you
>>> can.
>>> You cannot "convert" between the two except via "backup, re-init,
>>> restore", which probably is not what you have in mind.
>>> But as it is about a new installation of FreeBSD into a multi-OS
>>> setting, I'd suggest to leave everything untouched, install
>>> FreeBSD on its disk using GPT partitioning, and add a "chain loader"
>>> entry to GRUB configuration that boots FreeBSD. GRUB can understand
>>> both MBR and GPT, so it doesn't matter.
>> Something, possibly BSDinstall or, maybe something unknown made the 2
>> Windows 7 disks unbootable.  Great, now I can use them for something
>> other than adding weight to the box.
> Maybe there is just some damage to the bootcode of each "Windows".
> Suggestion: Unplug all disks except one of those (one at each time),
> boot with a "Windows" installation / repair DVD, restore the boot
> sector - should boot fine again.
> However, it sounds totally wrong that a FreeBSD installer even
> _touches_ disks that are not subject to the FreeBSD installation.
> I can image that adding boot code (single-boot or boot manager)
> to the 1st disk of a setup is possible, but what you're describing
> sounds just wrong. Not entirely impossible, but ...

I downloaded the FreeBSD DVD1.  Disabled USB 3.0 support in the "UEFI 
BIOS", as ASUS calls it.  Now, FreeBSD does not go into the xhci loop.

I chose the entire 3rd disk, ada2 for FreeBSD, accepted most of the 
defaults and the installation completed.  I did not see where BSDinstall 
offered a choice about the MBR.  However, I can not boot anything but 
FreeBSD.  So, BSDinstall did write something to ada0, I have not 
discovered what. I can boot HD0 from "UEFI BIOS"

Maybe BSDinstall messed with moterboard EFI boot???

> Also boot into Linux and make sure the GRUB configuration is
> correct.
>> I changed HD2, sdc to GPT with gparted.  I installed Ubuntu 18.04 on it.
>> I booted sda and used update-grub2.  Seemed to go OK, but I could not
>> get grub to boot sdc.  The boot menu listed sdc, but when selected igrub
>> actually booted sda.  Looking at boot/grub/grub.cfg, I see the menuentry
>> for sdc to have the same values as sda.
>> grub bug??
> Something went wrong when update-grub2 altered the configuration,
> I'd guess. You can manually change the GRUB configuration as needed.

I am trying very hard to not do anything non-automatic or not
out-of-the-box.  Getting old and I forget things...

Tom Dean

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