Re: BSD disklabel partition letters in NetBSD

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

> Sent: Thursday, October 04, 2018 at 9:10 PM
> From: "Don NetBSD" <netbsd-embedded%gmx.com@localhost>
> To: "NetBSD Users Mailing List" <netbsd-users%netbsd.org@localhost>
> Subject: Re: BSD disklabel partition letters in NetBSD

[...]

> I've never tinkered with moving swap out of 'b' -- but imagine it could be
> done, reliably.

According to some previous messages, it should: it is non-conventional, but
not forbidden.

> I'm not sure why you would need two DIFFERENT swap partitions as only one
> would be in use (based on which OS was booted).  But, let someone else
> argue that point.

Oh, actually you are right, it shouldn't be needed to duplicate also the
swap partitions, even because the amount of RAM is the same.

> You can specify which NetBSD partition to boot at the boot prompt.  Or,
> build a "menu" that provides a simpler interface to this.

Ok!

> fstab(5) in each root partition (/etc being part of that, in this example)
> would call out 'e' or 'h' as the partition to be mounted on /home in that
> particular root file system.  The "other" home partition could then be
> mounted somewhere else (assuming the filesystem type is supported by the
> kernels built for A/B.

Ok, and thank you also for the detailed fstab(5) example.

> The disklabel is the same for each (there's only one, in this case).  I am
> assuming that these are non-overlapping regions of the medium.  I.e., the
> physical sectors used by A's root partition differ from those used by B's.

Yes, of course: I didn't explicitly write it, but the disklabel partitions
of the example must be non-overlapping regions of the disk.

> So, set up those partitions (size+offset) as befitting your needs.  Then,
> just elect which to boot (boot prompt) and where to mount the others (fstab).

[...]

> The disklabel just cuts the medium into "pieces" (avoiding the term "slices").
> It doesn't know where those will be mounted

Ok, thanks for clarifying this. It was still a confusing issue, because
sometimes (also in sysinst(8)) when the BSD disklabel contents is shown, also
the mountpoints were listed, as if this information were stored in the
disklabel. But instead:

>  fstab(5)'s role is
> to specify these mount points

> (assuming you don't deliberately do something
> "outside" the normal approach -- like running a special script to mount stuff)

No, of course in this example we are referring to fstab(5) only, so a "standard"
usage.
Thank you so much!

Rocky