Re: install/47671: How do I manually add an extra MBR style disk?

[mlelstv%serpens.de@localhost (Michael van Elst)]

The following reply was made to PR install/47671; it has been noted by GNATS.

From: mlelstv%serpens.de@localhost (Michael van Elst)
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: install/47671: How do I manually add an extra MBR style disk?
Date: Thu, 21 Mar 2013 07:37:29 +0000 (UTC)

 andrew.cagney%gmail.com@localhost (Andrew Cagney) writes:
 
 >Here's the output from several further runs with -w:
 
 ># mbrlabel /dev/rsd0
 >Found MSDOS partition; size 1073741824 (524288 MB), offset 2048
 >  skipping existing MSDOS partition at slot a.
 >Found 4.2BSD partition; size 524288000 (256000 MB), offset 1073743872
 >  adding 4.2BSD partition to slot e.
 
 >5 partitions:
 >#        size    offset     fstype [fsize bsize cpg/sgs]
 > a: 1073741824      2048      MSDOS                     # (Cyl.      1 -
 >524288)
 > b:     16384 1073743872     4.2BSD   1024  8192    16  # (Cyl. 524289 -
 >524296)
 > c: 1952151552         0     unused      0     0        # (Cyl.      0 -
 >953198)
 > d:     16384 1073743872     4.2BSD   1024  8192    16  # (Cyl. 524289 -
 >524296)
 > e:     16384 1073743872     4.2BSD   1024  8192    16  # (Cyl. 524289 -
 >524296)
 
 >notice how it is breeding partitions ...
 
 That looks like a non-i386 system (c seems to be the raw partition)
 and a bug.
 
 For some reason mbrlabel forces the size of a BSD partition to 16384,
 which also defeats the duplicate detection. BSD partitions are those
 with an MBR type of
 
 165 MBR_PTYPE_386BSD
 166 MBR_PTYPE_OPENBSD
 168 MBR_PTYPE_APPLE_UFS
 169 MBR_PTYPE_NETBSD
 
 That's probably done because BSD partitions also use the other
 parameters (fsize,bsize,cpg/sgs) that can only be guessed without
 further analyzing the disk contents.
 
 The bug doesn't usually show up on i386 systems because the only
 BSD type MBR partition found is usually the raw partition which
 is ignored anyway.
 
 
 >A reboot, however, seems to have flushed what ever was going wrong:
 
 That's because 'w' alone doesn't write to the disk but only updates the
 in-core version of the disklabel.
 
 -- 
 -- 
                                 Michael van Elst
 Internet: mlelstv%serpens.de@localhost
                                 "A potential Snark may lurk in every tree."