Re: disklabel differences FreeBSD, DragonFly


:On Thu, Jul 27, 2006 at 02:21:59PM +0200, Joerg Sonnenberger wrote:
:> On Thu, Jul 27, 2006 at 08:39:37AM +0200, Andreas Klemm wrote:
:> > Later I wanted to mount the dfly filesystems on FreeBSD 6.1,
:> > of course still my main Unix ;-) But it wasn't possible.
:>
:> DragonFly disklabels allow 16 entries by default, FreeBSD still limits
:> it to 8. That's why you can't read it directly.
:>
:
:Hmm, for the sake of compatibility, wouldn't it have been an option,
:to add this extra bit to the end of the struct ?
:
: Andreas ///
:
:--
:Andreas Klemm - Powered by FreeBSD 6

The thing to note here is that FreeBSD had to make room for the
UFS1+UFS2 boot code, so it moved the boot code back to the point
where it abuts the 8-partition-sized disklabel.

So at least insofar as FreeBSD goes, the partition table cannot be
expanded to 16 partitions with UFS1+UFS2 boot code. I'm guessing
that it *could* be expanded to 16 partitions with UFS1 only or
UFS2 only boot code (assuming the boot code were relocated back
to where it was originally in FreeBSD-4/5 times, before UFS2 came
along).

With regards to simply recognizing a DragonFly partition... yes,
that would be easy to do. Since FreeBSD is now devfs-based, the
bit we had to steal to support 16 partitions in /dev isn't an issue.

I dunno if geom changes the equation any. Personally I have always
felt that 8 partitions is restrictive. My main home server has 10
and the main DragonFly box has 11.

There is another solution for FreeBSD folks, however. You *DO* have
four slices to play with. You can put a disklabel with 8 partitions
in it on each one (for 32 total). It isn't as convenient, but it does
work.

-Matt
Matthew Dillon
<dillon@xxxxxxxxxxxxx>
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