udev rules for mdadm cause boot hangs and md array malfunctions

[Adalberto]

Binary package hint: udev

Hi,
las week I upgraded ubuntu 9.10 to 10.04, and then installed 2 new hard drives and built a new md0 RAID1 array by means of mdadm, defining also a new mdadm.conf with just one line for md0, and a new entry in fstab for the mount point of md0.
Upon reboot, the boot process stopped saying it couldn't find the device for this new mount point; /proc/mdstat listed this new strange "md_d0" array, inactive, with one of the two drives which were part of my md0.
On further reboots, I noticed the drive "captured" this way by "md_d0" was randomly picked up between the two drives of md0.
This thread here: http://osdir.com/ml/linux-raid/2009-08/msg00219.html directed my to the solution.
So here's the content of my 85-mdadm.rules file, edited in order not to run mdadm --incremental for each and every array member found!!

cat /lib/udev/rules.d/85-mdadm.rules
# This file causes block devices with Linux RAID (mdadm) signatures to
# automatically cause mdadm to be run.
# See udev(8) for syntax
SUBSYSTEM=="block", ACTION=="add|change", ENV{ID_FS_TYPE}=="linux_raid*", \
 RUN+="/sbin/mdadm --assemble --scan"
#RUN+="/sbin/mdadm --incremental $env{DEVNAME}"
#AMC100922: caused malfunctions on preconfigured arrays!!

This way it works just fine.
Don't know if this error could be related to the upgrade from 9.10 to 10.04, as I didn't have any md array on 9.10, and only defined it after the upgrade to 10.04.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[sungaMagnus (sungam)]

Instead of applying Adalberto's patch

I found this http://ubuntuforums.org/showthread.php?p=11388915 and it works for me
tl;dr there is a race condition between assemble of the raid array and the check on the health of the array.

In file, /usr/share/initramfs-tools/scripts/mdadm-functions

Modify function from:
degraded_arrays()
{
        mdadm --misc --scan --detail --test >/dev/null 2>&1
        return $((! $?))
}

To:
degraded_arrays()
{
        udevadm settle
        mdadm --misc --scan --detail --test >/dev/null 2>&1
        return $((! $?))
}

[Diego Morales (dgmorales)]

I am not sure if they should be marked as duplicates, but see also https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/1335642 .