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: Wed, 20 Mar 2013 07:00:10 +0000 (UTC)

 andrew.cagney%gmail.com@localhost writes:
 
 >On systems that expect to have disks with MBR partitions (see fdisk(8))
 >disklabel will find, and update if requested, labels in the first 8k of
 >type 169 (NetBSD) MBR labels and within the first 8k of the physical
 >disk.
 [...]
 >On other systems disklabel will only look at the start of the
 >disk.
 
 This only defines the place where disklabel is looking for an existing
 BSD disklabel, it doesn't mean that it uses the MBR for anything else.
 
 
 So to add a MBR disk you
 
 - use fdisk to add a NetBSD partition to the MBR.
 - use disklabel (-i or -e) to create NetBSD partitions within the
   range of the raw partition 'c'. For a data disk that is usually only
   one partition 'e' (to avoid confusion with the root 'a' or swap 'b').
 
 and if necessary:
 
 - use mbrlabel to collect non-NetBSD partitions from the MBR into
   the BSD disklabel.
 
 
 
 >-- mbrlabel (assuming I'm meant to be using it)
 >It doesn't seem to let me specify which partitions should get which letters 
 >(a ended up being dos), or that it should start from scratch?
 
 mbrlabel does read the MBR and adds partitions to the existing BSD disklabel
 (the kernel has a default disklabel if it cannot read one from the disk).
 It will skip MBR partitions that already exist in the BSD disklabel.
 
 
 When I run mbrlabel it reads the MBR:
 
 Partition table:
 0: Primary DOS with 32 bit FAT - LBA (sysid 12)
     bootmenu: WinME
     start 16065, size 4049136 (1977 MB, Cyls 1-253/11/63)
 1: NetBSD (sysid 169)
     bootmenu: NetBSD
     start 4745201, size 151556287 (74002 MB, Cyls 295/95/42-9729/80/63), Active
 2: OS/2 hidden C: drive (sysid 132)
     bootmenu: Resume
     start 4065201, size 657909 (321 MB, Cyls 253/12/1-293)
 3: <UNUSED>
 
 and prints:
 
 | Found MSDOS partition; size 4049136 (1977 MB), offset 16065
 |   skipping existing MSDOS partition at slot h.
 
 MBR partition 0, already matches disklabel partition 'h'. Ignored.
 
 | Found 4.2BSD partition; size 151556287 (74002 MB), offset 4745201
 |   skipping existing unused partition at slot c.
 
 MBR partition 1, already matches disklabel partition 'c'. Ignored.
 
 | Found unknown partition; size 657909 (321 MB), offset 4065201
 |   adding unknown partition to slot j.
 
 MBR partition 2, no match in disklabel, create a new partition 'j'
 for it ('j' because that's the first free partition slot in the disklabel,
 i already have 'a' to 'i').
 
 Then it prints the resulting disklabel and depending on options may
 update the in-core disklabel and the one on the disk.
 
 If you don't have an existing disklabel, mbrlabel will fill the
 empty slots 'a', 'b', then 'e', etc. That's what you observeed.
 
 -- 
 -- 
                                 Michael van Elst
 Internet: mlelstv%serpens.de@localhost
                                 "A potential Snark may lurk in every tree."