Re: BSD disklabel partition letters in NetBSD

["Rocky Hotas" <rockyhotas%post.com@localhost>]

> Sent: Saturday, September 22, 2018 at 11:39 AM
> From: "Martin Husemann" <martin%duskware.de@localhost>
> To: "Rocky Hotas" <rockyhotas%post.com@localhost>
> Cc: "NetBSD Users Mailing List" <netbsd-users%netbsd.org@localhost>
> Subject: Re: BSD disklabel partition letters in NetBSD
>
> It is actually quite simple (with a few twists, muahahah :-}):

I guessed it :).

> You can check with "sysctl kern.rawpartition", it is 3 on these architectures.

Ok, thanks!

> Then there are architectures that traditionally required an MBR
> partitioning scheme (usually to cooperate with ancient other OSes), so
> you have to use fdisk before disklabel to partition a disk.

So, the distinction between systems that only reserve partition "c" and
those who also reserve partition "d" is the necessity to use MBR.
I wonder if in those systems one can install BSD disklabel to replace MBR
(without caring about incompatibilities with other OSs): and, if yes,
what would be the use of "c" and "d" when MBR doesn't exist at all.
In other words: with amd64, if it is possible to use the whole disk and
to install BSD disklabel as the only partition table, what would happen?

> All other partition letters are free for arbitrary use. Very common (but not
> mandatory) is "a" as root partition, and "b" as swap.

Ok!

> For the number of disklabel partitions: this depends on the architecture - 
> where the disklabel structure is shared itself with other OSes (say on Sun
> machines) we can not arbitrarily change it. On some others (e.g. VAX)
> there are size limitations due to boot code placement (or similar).

Like for `rawdisk', is there any other sysctl parameter with the number of
available partitions in the current system?

> Now, of course, this all became mood on most modern machines with the move
> to GPT, and this is good. As you probably know, we use full devices for
> these (dk* and rdk*), so no limiting alphabet nor reserved letters.

Despite vaguely knowing that GPT is replacing MBR and similar, I never
installed NetBSD with GPT, so I didn't know this.

> Martin

Thank you!

Rocky