Re: [email protected]

On Fri, 11 Mar 2022 07:15:54 -0500, Johannes Koehler <[email protected]> wrote:
> But... I went -fast- into flowing ground. I.e., I like to create more then
> one gpt partition table at one device (hybrid mbr?).

Would you try to create more than one master boot record on an mbr disk? Don't
try to create more than one gpt partition table per device.

When using gpt, there may optionally be an mbr. There are two types. Protective
and hybrid.

A protective mbr has one partition defined that covers the entire device. It's
purpose is ensure old partitioning software will think the entire drive is in
use, to help the user accidentally messing things up.

A hybrid mbr allows booting on old bios firmware systems that do not recognize
gpt partition tables. It's used to store the bootloader code such as stage 1
of grub.

Up-to-date versions of fdisk, sfdisk, cfdisk, etc. all work ok with gpt. Don't
use old partitioning software that doesn't handle gpt.

Other then knowing that gpt can handle a lot more partitions on a device than
mbr can, don't worry about partition numbers anymore. With gpt, there's no such
thing as extended or logical partitions. All partitions are primary partitions.

In most cases, such as during boot the partitions will be identified by it's UUID
(Universally unique identifier).

Be extremely careful when cloning disks to change the uuid on the new copy before
rebooting with both disks attached. Having non-unique UUIDs in the same system
makes it unpredictable which partition will be selected.

Since remembering a uuid is hard, in most cases a label may be used. Create a
label for each partition, again making sure it's unique, and use that instead
of the uuid to keep track of which partition is for what.

> The idea came into being... It was not possible to create more then three
> partitions into a newly created gpt header. The docs telling about up
> to 128 partitions. Menudriving@gdisk opens the way for this big amount
> of partion table entrys, but sgdisk not. I also wiped the mbr
> and gpt data before starting on with creating new partions using sgdisk
> with GUID tables.

That doesn't make sense. How old is the software you're using?

> Reading the manpages, and web resources mentioned in this gnu manpages,
> was not sufficient to understand the based numbering principle,
> and to work on knowledge without the wider sense of possible meanings.
> I.e to understand hybrid partitions.

Hope the above helps. Feel free to ask if anything isn't clear.

Regards, Dave Hodgins