[CentOS] CentOS 6.2 on partitionable mdadm RAID1 (md_d0) - kernel panic with either disk not present

Wed Jun 20 16:11:23 UTC 2012
Arun Khan <knura9 at gmail.com>

On Wed, Jun 20, 2012 at 10:06 AM, Arun Khan <knura9 at gmail.com> wrote:
> On Wed, Jun 20, 2012 at 1:00 AM,  <m.roth at 5-cent.us> wrote:
> .... snip ....
>> For one thing, edit grub.conf and get *rid* of that idiot rhgb and quiet,
>> so you can actually see what's happening. Sounds to me as though it's
>> trying to switch root to a real drive from the virtual drive of the ramfs,
>> and it's not working. One thing you *might* also try is before you boot,
>> edit the kernel line in grub, and add rdshell at the end, so you boot into
>> grub's rudimentary shell if/when it fails, and you can look around and
>> find what it's seeing.
> Will try your suggestion and report back.

As mentioned already there are no issues with both disks connected.
In this scenario, I have changed the "Partition ID" of the
partitionable RAID1 partitions  /dev/md_d0p1 and /dev/md_d0p2 to 'fd'
and then rebooted the system (recall earlier these partitions had

I also made the suggested changes to /boot/grub/grub.conf by Mark

Rebooted the system with both disks connected - system boots fine.
Messages are displayed including the md driver binding /dev/sda and
/dev/sdb.     The  "root" device /dev/md_d0p1 is detected and it is
mounted on / and life is hunky dory.

Reboot the system with disk1 removed, the kernel boots, the 'md'
driver  tries to bind sda.  At this point the systems seems to hang
for a few seconds and then 'dracut' reports that it cannot find
/dev/md_dop1 (the root partition)

         dracut Warning: No root device "block:/dev/md_d0p1" found

Console image pasted here <http://imagebin.org/217229>

In the "rdshell" environment I can see that /etc/mdadm.conf is defined
but beyond this I don't know what to look for.

Changing the Partition Id for the RAID1 partitions to 'fd' does not help.

Any further suggestions and/or comments?

-- Arun Khan