[Bug 1335642] Re: mdadm runs into infinite loop and prevents initrd/initramfs phase to finish on boot

[Jean-Marc Le Peuvedic]

Hello all!

Problem with same symptom (loops on the same massage).
My system boots on a USB stick and has 4 sata disks in RAID 5 with 3 active and a hot spare.  One of the disks failed and was kicked
out of the array (probably a transient failure, needs further investigation). For some reason I then lost all access means to the machine, although Apache was still responding. The machine did not react to an ACPI reboot and I hard rebooted it while it was rebuilding the RAID on the spare disk ...  
It should have come up fine on 2 disks, but instead was stuck with the four line beginning with "Incrementally starting RAID arrays". 
Some keying after boot in recovery mode lets me down to a root shell on initdisk. I can see that the RAID is active forced read only on two disks out of three.  If I stop it and assemble it again from the working disks, it is just active, ready to go and can be mounted. 
I have re-added the failed and spare partitions: if the failing one fails again rebuilding will proceed on the hot spare.  Reconstruction of the missing RAID component is ongoing.

I have operated Linux RAID setups for many years and I have had several
disk failures, some transient, some final. The boot scripts can handle
that in 10.04 LTS and 12.04 LTS. In 14.04 LTS something changed: it may
be mdadm choosing by default to assemble the array read only?

Hoping to provide useful information.

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https://bugs.launchpad.net/bugs/1335642

Title:
  mdadm runs into infinite loop and prevents initrd/initramfs phase to
  finish on boot

Status in “mdadm” package in Ubuntu:
  Confirmed

Bug description:
  Hi all,

  probably the issue is caused by changing the SATA-port where RAID
  disks were originally attached -- this is the only thing that happened
  before my Ubuntu 14.04 (kernel-3.13.0-27) became unbootable.

  During the boot the OS runs into infinite loop reporting from time to
  time these:

  incrementally starting raid arrays
  mdadm: Create user root not found
  mdadm: create group disk not found
  incrementally started raid arrays

  Since mdadm is in initrd image, I don't even know how to skip mdadm --
  workarounds are very welcome, please!

  For example, renaming /etc/mdadm/mdadm.conf in initrd image didn't
  help, mdadm then just repeats infinitely without group/user-related
  errors:

  incrementally starting raid arrays
  incrementally started raid arrays
  incrementally starting raid arrays
  incrementally started raid arrays
  ...

  Disks are successfully assembled into a RAID under LiveCD Ubuntu 13
  (yes , i have only old CD here)

  Why I consider this a bug? because my RAID-array is needed at
  application level, not on OS-level (e.g. it is not mounted as / or
  /boot). So, if one can't boot into OS it is a serious bug. Last but
  not least, I was never choosing to put mdadm into initramfs, so it is
  a decision taken by default that leads to not-bootable system...

  UPDATE1:
  in scripts/mdadm-functions of initrd image i see this:

  mountroot_fail()
  {
      message "Incrementally starting RAID arrays..."
      if mdadm --incremental --run --scan; then
          message "Incrementally started RAID arrays."
          return 0
      else        
          if mdadm --assemble --scan --run; then
              message "Assembled and started RAID arrays."
              return 0
          else
              message "Could not start RAID arrays in degraded mode."
          fi
      fi
      return 1
  }

  i tried 'mdadm --incremental --run --scan -c <path to
  etc/dmadm/dmadm.conf of initrd image> -v' and it exits silently
  without creating /dev/md/127 as I have expected.

  Whereas

  sudo mdadm --assemble --run --scan -c ./etc/mdadm/mdadm.conf -v

  Does the job. Is it an issue just of incremental mode?

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