[Bug 1077650] Re: booting from raid in degraded mode ends in endless loop

[Bernd Schubert]

Today a disk did not come up anymore in the morning and I just noticed that the bug is not fixed yet in mdadm-3.2.5-5ubuntu4.1. 
In fact, it got worse "bootdegraded=yes" is now default (ubuntu 14.04) and cannot be disabled anymore and so the system stays in an endless loop of "mdadm: CREATE group disk not found" messages. The only chance to survice the system was to boot a rescue system. As I didn't have a spare disk I had to get the system to boot in degraded mode.

Below some diagnostics. Please note, I'm not familiar at all how the
Ubuntu initramfs scripts are assembled from their pieces.

Diagnostic 1) In /usr/share/initramfs-tools/scripts/mdadm-functions

I disabled (commented out) the incremental if-branch
( mdadm --incremental --run --scan; then), instead only the assemble mdadm command run. After re-creating the initramfs and rebooting the  "mdadm: CREATE group disk not found" message was only shown *once*,  it then complained that it didn't find root partition and dropped to the busybox shell. MUCH BETTER!
Investigating on the shell I noticed that md devices had been assembled in degraded mode. Also,  running "mdadm --assemble --scan --run" and it brought up the same disk group message. So seems to be a bug in mdadm to show this message and to return an error code.
After running "vgchange -ay" I could leave the shell and continue to boot

Diagnostic 2) I now changed several things as we needed this system to
boot up automatically

2.1) I mad mountroot_fail to *always* execute 'vgchange -ay'

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

      # note, if someone does that, she probably should change it to vgchange -ay || true
    vgchange -ay
 
    return  mount_root_res
}


2.2) /usr/share/initramfs-tools/scripts/init-premount/mdadm

case mountroot_fail  now exits with 0, not with the exist code of
mountroot_fail

case $1 in
# get pre-requisites
prereqs)
        prereqs
        exit 0
        ;;
mountfail)
        mountroot_fail
        exit 0
        ;;
esac

. /scripts/functions


I think that is all I changed and the system now boots up in degraded mode like a charm.

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https://bugs.launchpad.net/bugs/1077650

Title:
  booting from raid in degraded mode ends in endless loop

Status in “mdadm” package in Ubuntu:
  Confirmed

Bug description:
  Its basically the same as reported here:

  http://efreedom.com/Question/6-103895/Can-Boot-Degraded-Mdadm-Array

  So I just installed a new system, which is supposed to get later on an
  additional disk. For now I created md raid1 devices with one disk
  missing. To get ubuntu booting at all without complaining about a
  missing disk I already added "bootdegraded=yes" to the kernel command
  line. And now it ends in an endless loop of

  unused devices: <none>
  Attempting to start the RAID in degraded mode...
  mdadm: CREATE group disk not found
  Started the RAID in degraded mode.

  ProblemType: Bug
  DistroRelease: Ubuntu 12.10
  Package: initramfs-tools 0.103ubuntu0.2
  ProcVersionSignature: Ubuntu 3.5.0-17.28-generic 3.5.5
  Uname: Linux 3.5.0-17-generic x86_64
  ApportVersion: 2.6.1-0ubuntu3
  Architecture: amd64
  Date: Sun Nov 11 16:26:55 2012
  PackageArchitecture: all
  ProcEnviron:
   LANGUAGE=en
   TERM=xterm
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: initramfs-tools
  UpgradeStatus: Upgraded to quantal on 2012-01-08 (308 days ago)

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