Re: Can't reboot after power failure (RAID problem?)

[Andrew Reid <reidac@bellatlantic.net>]

On Monday 31 January 2011 10:51:04 davidg@alcor.concordia.ca wrote:
> I posted in a panic and left out a lot of details.  I'm using Squeeze, and
> set up the system about a month ago, so there have been some upgrades.  I
> wonder if maybe the kernel or Grub was upgraded and I neglected to install
> Grub again, but I would expect it to automatically be reinstalled on at
> least the first disk.  If I remove either disk I get the same error
> message.
>
> I did look at /proc/cmdline.  It shows the same uuid for the root device
> as in the menu, so that seems to prove it's an MD device that isn't ready
> since my boot and root partitions are each on MD devices.  /proc/modules
> does show md_mod.

  What about the actual device?  Does /dev/md/0 (or /dev/md0, or whatever)
exist?  

  If the module is loaded but the device does not exist, then it's possible
there's a problem with your mdadm.conf file, and the initramfs doesn't
have the array info in it, so it wasn't started.

  The easy way out is to boot from a rescue disk, fix the mdadm.conf
file, rebuild the initramfs, and reboot.

  The Real Sysadmin way is to start the array by hand from inside
the initramfs.  You want "mdadm -A /dev/md0" (or possibly
"mdadm -A -u <your-uuid>") to start it, and once it's up, ctrl-d out
of the initramfs and hope.  The part I don't remember is whether or
not this creates the symlinks in /dev/disk that your root-fs-finder
is looking for.

  It may be better to boot with "break=premount" to get into the 
initramfs in a more controlled state, instead of trying to fix it 
in the already-error-ed state, assuming you try the initramfs 
thing at all.

  And further assuming that the mdadm.conf file is the problem,
which was pretty much guesswork on my part...

					-- A.  
-- 
Andrew Reid / reidac@bellatlantic.net