disklabel differences FreeBSD, DragonFly

Matthew Dillon dillon at apollo.backplane.com
Fri Jul 28 22:36:31 UTC 2006

: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

    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

					Matthew Dillon 
					<dillon at backplane.com>

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