mdadm fails to assemble my RAID device

tomhildebrand · 06-25-2007, 02:22 AM

My Fedora FC6 system has 3 RAID devices
md0 RAID1 hosting the /boot filesystem
md1 RAID5 hosting the / filesystem
md2 RAID5 hosting the /usr2 filesystem
md0 recently failed with one bad disk preventing me from booting up. Instead of working around the single failure it gives me "cannot start dirty degraded array for md1". But it doesn't matter, I wanted to re-image anyway. But I would like to get my md2 back (700GB of precious files). When starting the machine with a Knoppix livecd, the disk partitions making up md2 (/dev... hda2 hdc2 hde2 hdg2) appear to be healthy, but mdadm fails to assemble the array.

root@Knoppix:/# mdadm --assemble --scan
mdadm: error opening /dev/md0: No such file or directory
mdadm: error opening /dev/md2: No such file or directory
mdadm: error opening /dev/md1: No such file or directory

I read in another thread that I should manually create /dev/md2, but that didn't help.
root@Knoppix:/# mknod /dev/md0 b 9 0
root@Knoppix:/# mknod /dev/md1 b 9 1
root@Knoppix:/# mknod /dev/md2 b 9 2
root@Knoppix:/# ls -al /dev/md*
brw-r--r-- 1 root root 9, 0 Feb 21 21:19 /dev/md0
brw-r--r-- 1 root root 9, 1 Feb 21 21:19 /dev/md1
brw-r--r-- 1 root root 9, 2 Feb 21 21:19 /dev/md2
root@Knoppix:/#
root@Knoppix:/# mdadm --assemble --scan
mdadm: error opening /dev/md0: No such device or address
mdadm: error opening /dev/md2: No such device or address
mdadm: error opening /dev/md1: No such device or address

Any help would be greatly appreciated.

fayez · 06-25-2007, 09:10 AM

try this one:

root@Knoppix:/# mdadm --assemble /dev/md2 /dev/hda2 /dev/hdc2 /dev/hde2 /dev/hdg2

tomhildebrand · 06-26-2007, 12:11 AM

Thanks for your help. But it's still not working. Here's what I get:

Code:

root@Knoppix:/# mdadm --assemble /dev/md2 /dev/hda2 /dev/hdc2 /dev/hde2 /dev/hdg2
mdadm: error opening /dev/md2: No such device or address

But strangely, /dev/md2 seems to exists

Code:

root@Knoppix:/# ls -al /dev/md*
brw-rw---- 1 root disk 9, 2 Jun 25 18:08 /dev/md2

So I tried something suggested in another thread:

Code:

root@Knoppix:/etc/init.d# mdadm --examine --scan /dev/hd*2 >/etc/mdadm/mdadm.conf
root@Knoppix:/etc/init.d# cat /etc/mdadm/mdadm.conf
ARRAY /dev/md2 level=raid5 num-devices=4 UUID=e46f59e0:9cdca28f:f98ddb8f:1d0eb62c
root@Knoppix:/etc/init.d# /etc/init.d/mdadm start
root@Knoppix:/etc/init.d# /etc/init.d/mdadm-raid start
Assembling MD arrays...done (disabled in /etc/default/mdadm).
root@Knoppix:/etc/init.d# cat /proc/mdstat
cat: /proc/mdstat: No such file or directory

So, still no RAID array according to /proc/mdstst.
More alarmingly: Why is there no /proc/mdstst at all?
Is the RAID service not running? Should I start it manually? How?

Any ideas?

Thanks.

fayez · 06-26-2007, 06:20 AM

Then the md driver did not loaded, try to load the md driver again,

now I cann't remember the commands I am sorry....

fayez · 06-26-2007, 06:34 AM

I think the commands:

# lsmod
to list loaded modules, and
# modprobe md
to load the md module

try it out..........

tomhildebrand · 06-27-2007, 12:14 AM

Fayez,
THANK YOU, THANK YOU, THANK YOU !

That did it.
I couldn't imagine that the kernel module for the md driver wouldn't be loaded when Knoppix starts, but it isn't. Loading the md kernel module per your instructions solved that problem, I can see /proc/mdstat and all the md commands work. Most importantly: I got my files back.

Thanks again.

fayez · 06-28-2007, 12:08 AM

Any time man, and remember we all use this useful forum to help each other...