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

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

From: (Michael van Elst)
Subject: Re: install/47671: How do I manually add an extra MBR style disk?
Date: Wed, 20 Mar 2013 07:00:10 +0000 (UTC) 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
 >On other systems disklabel will only look at the start of the
 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
                                 "A potential Snark may lurk in every tree."

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