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

[Paul Crawford]

I think this applies to the following versions since I first tested the 1.61 version of os-prober to see if it was already fixed (was not) and my patach should work for all of them, though I have only tested on 1.51 & 1.61:
Saucy (1.61ubuntu1)
Raring (1.57ubuntu1)
Quantal (1.56ubuntu1)
Precise (1.51ubuntu3)
The patch is not ideal, for example, it has not fixed the on_sataraid() function to avoid probing components of a mdadm array (as it does for dmraid arrays), though later they are skipped if found in /proc/mdstat 
It also presumes the md arrays are up to be probed. This last point is not unreasonable as activating potential arrays for probing may be hazardous if they had been stopped for other maintenance reasons.

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Title:
  update-grub fails to detect other md OS

Status in “grub2” package in Ubuntu:
  New
Status in “os-prober” 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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