[Bug 1217933] Re: update-grub fails to detect other md OS

[Paul Crawford]

I think I have a patch that fixes this, basically adding another step to
generate the 'partitions' that include the md arrays, and to drop the md
arrays themselves as being part of any array obtained from /proc/mdstat

If this is OK, can it be made available for 12.04 support?

** Patch added: "Update for os-prober to detect mdadm RAID"
   https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1217933/+attachment/3793028/+files/detect-mdadm.diff

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Title:
  update-grub fails to detect other md OS

Status in “grub2” package in Ubuntu:
  New

Bug description:
  I have a system with two main HDD configured as several md RAID-1 devices and I installed the 32-bit version of 12.04.2 on to one of these partitions (using the "alternate installer" ISO), with most of the others being user data (e.g. one for /home, another for virtual machines, etc). I had one md partition free and then installed the 64-bit version (12.04.3) on to that, again using the alternate installer.
  However, after the installation it is unaware of the 1st system, so running update-grub fails to add that to the boot menu and I am not able to dual-boot 32 & 64 bit systems. This worked OK previously with a hardware RAID card, but that was true hardware RAID and presented the disks as a single SCSI device.

  $ lsb_release -rd
  Description:	Ubuntu 12.04.3 LTS
  Release:	12.04

  $ apt-cache policy multipath-tools
  multipath-tools:
    Installed: (none)
    Candidate: 0.4.9-3ubuntu5
    Version table:
       0.4.9-3ubuntu5 0
          500 http://gb.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

  I expect the OS probing to detect other operating systems, in
  particular to detect another instance of Ubuntu.

  Additional information:
  $ more /proc/mdstat 
  Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
  md1 : active raid1 sda3[0] sdb3[1]
        72427392 blocks super 1.2 [2/2] [UU]
        
  md2 : active raid1 sda6[0] sdb6[1]
        51167104 blocks super 1.2 [2/2] [UU]
        
  md0 : active raid1 sda1[0] sdb1[1]
        2046912 blocks super 1.2 [2/2] [UU]
        
  md4 : active raid1 sda8[0] sdb8[2]
        307068736 blocks super 1.2 [2/2] [UU]
        
  md3 : active raid1 sda7[0] sdb7[1]
        1023868736 blocks super 1.2 [2/2] [UU]

  $ mount | grep '^/dev/' | sort
  /dev/md1 on / type ext4 (rw,errors=remount-ro)
  /dev/md3 on /home type ext4 (rw)
  /dev/md4 on /vm type ext4 (rw,nobarrier)
  /dev/sdc5 on /scratch type ext4 (rw,nobarrier)

  NOTE: sda & sdb form the md devices but sdc is not part of any RAID,
  md0 is unused (was planned for /boot but not used), and md2 has the
  32-bit '/' partition which can still be mounted and accessed.

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