[Bug 713874] Re: grub misinterprets md/raid device

[Matt Mossholder]

Yeah, this has bitten me too. GRUB2 is looking for md devices to use the
new style /dev/md/# device naming, rather than the old /dev/md# style.
As a short-term fix, simply creating the /dev/md directory, and creating
symlinks to the actual device nodes seems to work.

Example:

mkdir /dev/md
ln -s /dev/md0 /dev/md/0

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Title:
  grub misinterprets md/raid device

Status in “grub2” package in Ubuntu:
  Confirmed

Bug description:
  Binary package hint: grub2

  I have a RAID5 mdadm array on /dev/md0. It is fully functional but I
  cannot boot from it because grub detects it as "/dev/md/0" (with an
  extra slash). Running "update-grub", for example, produces a grub.cfg
  with the lines "set root='(md/0)'". Upon rebooting, grub reports
  "error: file not found" and drops into a rescue shell.

  Some (or all) disks in this array were previously used in a RAID array
  using mdadm metadata version 0.90. Now, however, they are using
  version 1.20. Since mdadm puts metadata v1.20 in a different location,
  I wonder if perhaps there's a ghost of the old 0.90 metadata hanging
  around, which is confusing grub.

  $ sudo mdadm --detail --scan
  ARRAY /dev/md0 metadata=1.2 name=eve:0 UUID=98ab8ad1:23e4df2e:d8bb3605:b9be0e1f

  $ sudo mount /dev/md0 /mnt/raid
  $ sudo mount --bind /dev /mnt/raid/dev
  $ sudo mount --bind /dev/pts /mnt/raid/dev/pts
  $ sudo mount --bind /proc /mnt/raid/proc
  $ sudo mount --bind /sys /mnt/raid/sys
  $ sudo chroot /mnt/raid
  # ls -l /dev/md*
  brw-rw---- 1 root disk 9, 0 2011-02-06 11:14 /dev/md0
  # cat /proc/mdstat 
  Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] 
  md0 : active raid5 sdc1[1] sda1[0]
        968576000 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/2] [UU_]
  # grub-mkconfig | grep 'set root'
  Generating grub.cfg ...
  set root='(md/0)'
  Found linux image: /boot/vmlinuz-2.6.35-25-generic
  Found initrd image: /boot/initrd.img-2.6.35-25-generic
  	set root='(md/0)'
  	set root='(md/0)'
  Found linux image: /boot/vmlinuz-2.6.35-24-generic
  Found initrd image: /boot/initrd.img-2.6.35-24-generic
  	set root='(md/0)'
  	set root='(md/0)'
  Found linux image: /boot/vmlinuz-2.6.35-23-generic
  Found initrd image: /boot/initrd.img-2.6.35-23-generic
  	set root='(md/0)'
  	set root='(md/0)'
  Found linux image: /boot/vmlinuz-2.6.35-22-generic
  Found initrd image: /boot/initrd.img-2.6.35-22-generic
  	set root='(md/0)'
  	set root='(md/0)'
  Found linux image: /boot/vmlinuz-2.6.32-25-generic
  Found initrd image: /boot/initrd.img-2.6.32-25-generic
  	set root='(md/0)'
  	set root='(md/0)'
  Found memtest86+ image: /boot/memtest86+.bin
  	set root='(md/0)'
  	set root='(md/0)'
  Found Microsoft Windows XP Home Edition on /dev/sdb1
  	set root='(hd1,msdos1)'
  done

  $ lsb_release -rd
  Description:	Ubuntu 10.10
  Release:	10.10

  $ apt-cache policy grub-pc mdadm
  mdadm:
    Installed: 2.6.7.1-1ubuntu16
    Candidate: 2.6.7.1-1ubuntu16
    Version table:
   *** 2.6.7.1-1ubuntu16 0
          500 http://mirror.aarnet.edu.au/pub/ubuntu/archive/ maverick/main amd64 Packages
          500 http://au.archive.ubuntu.com/ubuntu/ maverick/main amd64 Packages
          100 /var/lib/dpkg/status
  grub-pc:
    Installed: 1.98+20100804-5ubuntu3
    Candidate: 1.98+20100804-5ubuntu3
    Version table:
   *** 1.98+20100804-5ubuntu3 0
          500 http://mirror.aarnet.edu.au/pub/ubuntu/archive/ maverick/main amd64 Packages
          500 http://au.archive.ubuntu.com/ubuntu/ maverick/main amd64 Packages
          100 /var/lib/dpkg/status

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