mdadm fails to assemble my RAID device

[TKH]

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

Another suggestion yielded no success:

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

And no luck with this suggestion either:

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

Why is there no /proc/mdstst at all?
Is the RAID service not running? Should I start it manually? How?

Any ideas?

Thanks.

[multescugeorge@]

Perhaps knoppix has problems with raid. try the Fedora cd1 (or the dvd) in linux rescue mode, see if it finds something.

[TKH]

Problem solved. Forum member Fayez suggested that the md kernel module mught not be loaded when Knoppix starts up. That was it. I loaded the module with
modprobe md
and all of a sudden all the md commands worked properly.
And I got my files back :-)

Thanks again for everyone's help.