[Bug 158918] Re: [->UUIDudev] installing mdadm (or outdated mdadm.conf) breaks bootup

[Roy Helge Rasmussen]

This bug has bugged me for a while now. It started in 10.10 and is still
there in 11.04.

Fresh install of Natty, 11.04 AMD64. All updates performed. -> Reboot
works fine.

Install MDADM -> reboot fails

mount: mounting /dev/disk/by-uuid/.... on /root
failed: Device or resource busy
...
...
No init found. Try passing init=bootarg.

Remove MDADM (boot on live-CD) -> reboot works fine


System has 7 disks. /dev/sda as boot disk. /dev/sd[bcdefg] are used as raid members.

Error occurs both when a raid is properly set up, and when all raid
members have the superblock zeroed. Error occurs both when mdadm.conf is
correct or blank, or missing.

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Title:
  [->UUIDudev] installing mdadm (or outdated mdadm.conf) breaks bootup

Status in “mdadm” package in Ubuntu:
  Triaged

Bug description:
  Original Report (also confirmed with 9.10 and 10.04 beta1):

  On a freshly installed ubuntu-7.10-alternate, with latest apt-get
  update.

  When the 'mdadm' package is installed, the system fails to boot
  successfully, and ends up at the initrd '(busybox)' prompt.

  Hardware: DELL 1950 - 1RU Server
  HDD: SAS

  To get the server booting again you need to revert to the old
  initramfs:

  - Boot with ubuntu-7.10-alternate, and go through install steps up to 'partitioning'.
  - ALT-F2 to start other shell
  - 'fdisk -l' to see details of available drives.
  - mkdir /mnt/disk
  - mount -t ext3 /dev/sdb1 /mnt/disk
  - cd /mnt/disk/boot
  - mv initrd-<version>.img initrd-<version>.img-new
  - cp initrd-<version>.img.bak initrd-<version>.img
  - sync
  - reboot

  ---
  Diagnose:

  -> This is mdadm setting up arrays according to unreliable superblock
  information (device "minor" numbers, labels, hostnames) combined with
  the idea of fixing the unreliability by limiting array assembly with
  information from mdadm.conf (PARTITIONS, ARRAY, HOMEHOST lines) which
  just reassigns the unsolvable conflict handling problem to setup
  tools, admins and installers. It forces them to create mdadm.conf
  files. And of course they fail.

  In cases where old superblocks are found on the disks during mdadm
  install, they are added to ARRAY definitions  (that really shouldn't
  need to be there at all) in mdadm.conf, and copied over into the
  initramfs. During next boot the system can not assemble these
  (incomplete) arrays.

  Cure:

  Systematically prevent conflicts from arising instead of relying on
  mdadm.conf maintanance. -> Do not depend on mdadm.conf definitions but
  use UUID-based array assembly as described in comment #33

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