On Thu, Apr 7, 2022 at 5:21 PM Neal Gompa <ngompa13(a)gmail.com> wrote:
On Thu, Apr 7, 2022 at 7:10 PM Demi Marie Obenour <demiobenour(a)gmail.com> wrote:
> Can the disk be partitioned so that it is valid for *both* MBR
and GPT?
>
There are two options here: protective MBR and hybrid MBR.
Protective MBRs are well-supported and I believe created by default
when you create a GPT partitioning scheme for BIOS systems already
with Anaconda. I think it's done with UEFI as well, but if not, we can
certainly force it.
The second option is known as hybrid MBR. The gdisk utility can create
them:
https://www.rodsbooks.com/gdisk/hybrid.html
Needless to say, it's... interesting... I'm not sure if more tools
support hybrid MBRs since this was last refreshed in 2019.
It's also kinda scary and not really necessary unless you need to
interoperate with OSes that expect MBR in a mixed BIOS+UEFI boot
setup.
Strictly speaking per the UEFI spec, hybrid MBR's don't exist.
Creating such a thing means it's really MBR and the GPT is invalid,
and it requires all software to treat it as such. The only valid MBR
with a valid GPT, is a protective MBR (PMBR) which is defined as
having one partition the size of the device or the maximum size
supported by MBR if the device is bigger.
--
Chris Murphy