[Bug 541058] Re: [->UUIDudev] mdadm fails to automatically assemble raid during boot (without mdadm.conf)

[rooijan]

Just an update for everyone interested.  I solved my issue by one(or
multiple) of the following steps.  Failing my sdc disk, pasting new
superblock, writing new boot sector, partitioning again and adding the
disk back.  So I am still not sure what caused my problem except I am
fairly sure that my 2nd disk had a previous superblock that confused
things. Disk was used in another system as part of a md array.  What
showed me the issue was "mdadm -Es".  It showed me two arrays that can
be assembled.

Sorry I can not be more helpful except you should run mdadm -Es early on
and avoid a lot of tail chasing.  If you are seeing an array you did not
expect that will cause the problems with "--incremental" when booting
up.

Before I fixed the issue I was seeing this:
root at jamaica:~# mdadm --examine --scan
ARRAY /dev/md0 UUID=5551e210:6dbc9e1b:2aa365fc:c3f97a4c
ARRAY /dev/md0 UUID=4795c86a:79111507:dbd3f904:98c17f24

After:
root at jamaica:~# mdadm --examine --scan
ARRAY /dev/md0 UUID=4795c86a:79111507:dbd3f904:98c17f24

Also worth noting is my superblock is 0.90.

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https://bugs.launchpad.net/bugs/541058

Title:
  [->UUIDudev] mdadm fails to automatically assemble raid during boot
  (without mdadm.conf)

Status in “mdadm” package in Ubuntu:
  In Progress

Bug description:
  Binary package hint: mdadm

  Creating an mdadm array works fine:
  mdadm --create /dev/md0 -n 3 -l5 /dev/sdb1 /dev/sdc1 /dev/sdd1
  Now when booting the array is assembled correctly.

  Delete the array and zero-superblock, create new partition and mark as "fd", create the same array again with command above.
  Now the system tries to assemble a single device into /dev/md_d0 - when other devices are missing.

  I checked each device with -examine and each reports the same uuid, the same host and the same name.
  In order to get it working one has to stop the md_d0 and assemble manually:
  mdadm --stop /dev/md_d0
  mdadm --assemble /dev/md0 /dev/sdb1 /dev/sdc1 /dev/sdd1

  To overcome this problem one has to remove the homehost from mdadm.conf and assemble the array manually during boot.
  What helps ist to reinstall the system ...

  This bug is pretty often found when googling around. Possible hints
  are udev and dmraid, whereas I already deinstalled dmraid but didn't
  help.

  Ubuntu 9.10 Linux 2.6.31-14-generic-pae
  mdadm 2.6.7.1

  * The array gets configured when mdadm.conf reflects the array
  definitions. But it does not get assembled automatically

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