Re: Use of disklabel, MBR and GPT

[Rocky Hotas <rockyhotas%firemail.cc@localhost>]

On ott 16 12:25, Martin Husemann wrote:
> I have a few clarifications...

Thanks for writing them.

> > Maybe this is trivial, but during the installation of NetBSD a
> > disklabel is actually nested inside a primary MBR partition.
> 
> This is true for some architectures (like amd64), but others do use plain
> disklabel on a disk without any MBR. This also works on amd64 when you
> do not need to boot from the disk.

Yes, exactly. I tried to specify this (``Note that the above behaviour
is about amd64; for other ports it may change''), maybe I could have
better positioned the sentence.

> > - to grant the compatibility with PC/DOS (and other OSs like Windows
> >   this way can still use the same disk);
> > - to grant a regular boot on PC/IBM hardware (where, without a valid
> >   MBR, the BIOS could not even try to search a bootloader on the disk).
> 
> Yes and no - newer sysinst versions allow to kill the whole disk content
> (including the MBR and whatver partitions exists), and start from scratch
> (as if the disk had been totaly wiped before). Use with care - this kills
> all data on the disk.

Oh, ok, maybe I did not dig enough in newer installers.

> The (single) disklabel can then describe partitions outside of the NetBSD
> partition too (as seen when setting up (U)EFI booting on disks with MBR
> partitioning -  the EFI boot partition shows up in the disklabel).

Thanks for pointing out this.

> That is kind of correct once the kernel is running.

Yes, I was meaning this.

> This is not true - you can select GPT for boot disks with both firmwares.

Ops, again my fault about newer installers.

> You did not stress the (from my POV) most important points of all this mess:
> 
>  - if you need the disk to be accessible from other systems, you need to
>    use a partitioning scheme they understand. MBR works for DOS and older
>    windows, GPT works for nearly everything newer. Disklabel only works
>    for older Unix systems or NetBSD.

I did not specify this about GPT, but as regards MBR DOS compatibility... the
whole message is about this topic. Maybe a recap was missing.

>  - if your disk is larger than 2TB you can not use MBR (you may have luck
>    with some systems upto 4TB, but the "portability" is lost), nor can
>    you use disklabel. Select GPT (sysinst knows about the size limits
>    and will avoid non-working selections).
> 
> The topic is confusing, thanks for summarizing!

Thanks to you for all the clarifications and integrations.

Rocky