[Bug 573477] Re: Mdadm array fails to assemble on boot.

[RussianNeuroMancer]

Same problem here. Solved by adding to /etc/mdadm/mdadm.conf this line:
ARRAY /dev/md1 metadata=1.2 UUID=someuuid name=somename:0

/dev/md1 may be different for you. It' may be md/1, md1 or something.
I get someuuid by using blkid utility.
somename from mdadm --detail /dev/md1

To get information from dlkid and mdadm --detail you need to stop array first
mdadm --stop /dev/md1
and then assemble it again:
sudo mdadm --assemble /dev/md1 /dev/sdX1 /dev/sdY1
After that you will able to get UUID and array name.

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https://bugs.launchpad.net/bugs/573477

Title:
  Mdadm array fails to assemble on boot.

Status in “mdadm” package in Ubuntu:
  Confirmed

Bug description:
  Binary package hint: mdadm

  On boot I receive a message stating 'the disk for/mnt/md0 is not ready
  yet or not present. Continue to wait; or Press S to skip mount or M
  for manual recovery'. If i press M and try 'mount -a' it states that
  'special device /dev/md0 does not exist'. If I try 'mdadm --assemble
  --scan' it states 'no devices found for /dev/md0'. If I skip the
  mounting of the array, and start the array then mount it through
  palimpsest everything mounts as should be (devices in array and mount
  location).

  Output of 'mdadm -D /dev/md0'

  /dev/md0:
          Version : 01.02
    Creation Time : Mon Nov 16 12:30:36 2009
       Raid Level : raid5
       Array Size : 1465151424 (1397.28 GiB 1500.32 GB)
    Used Dev Size : 976767616 (931.52 GiB 1000.21 GB)
     Raid Devices : 4
    Total Devices : 4
  Preferred Minor : 0
      Persistence : Superblock is persistent

    Intent Bitmap : Internal

      Update Time : Sun May  2 15:58:29 2010
            State : active
   Active Devices : 4
  Working Devices : 4
   Failed Devices : 0
    Spare Devices : 0

           Layout : left-symmetric
       Chunk Size : 64K

             Name : :raid5
             UUID : 02bcfe3b:44fc949f:f5f7e481:a421a2c0
           Events : 55496

      Number   Major   Minor   RaidDevice State
         0       8       49        0      active sync   /dev/sdd1
         1       8       33        1      active sync   /dev/sdc1
         2       8       17        2      active sync   /dev/sdb1
         4       8        1        3      active sync   /dev/sda1

  
  Contents of /etc/mdadm/mdadm.conf:

  # mdadm.conf
  #
  # Please refer to mdadm.conf(5) for information about this file.
  #

  # by default, scan all partitions (/proc/partitions) for MD superblocks.
  # alternatively, specify devices to scan, using wildcards if desired.
  DEVICE partitions

  # auto-create devices with Debian standard permissions
  CREATE owner=root group=disk mode=0660 auto=yes

  # automatically tag new arrays as belonging to the local system
  HOMEHOST <system>

  # instruct the monitoring daemon where to send mail alerts
  MAILADDR server

  # definitions of existing MD arrays
  ARRAY /dev/md0 level=raid5 metadata=1.2 num-devices=4 UUID=02bcfe3b:44fc949f:f5f7e481:a421a2c0 name=md0

  # This file was auto-generated on Sat, 01 May 2010 18:15:04 +1000
  # by mkconf $Id$

  
  Contents of /etc/fstab

  # /etc/fstab: static file system information.
  #
  # Use 'blkid -o value -s UUID' to print the universally unique identifier
  # for a device; this may be used with UUID= as a more robust way to name
  # devices that works even if disks are added and removed. See fstab(5).
  #
  # <file system> <mount point>   <type>  <options>       <dump>  <pass>
  proc            /proc           proc    nodev,noexec,nosuid 0       0
  # / was on /dev/sda1 during installation
  UUID=906694f9-9425-4ae3-88cc-bd9f4161846b /               ext4    errors=remount-ro 0       1
  # swap was on /dev/sda5 during installation
  UUID=01cb5d34-e4ac-4329-95c1-e9396a414a28 none            swap    sw              0       0
  #mdadm array
  /dev/md0	/mnt/md0	auto	defaults	0	0

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