UBUNTU: apt-get install mdadm

cat

http://www.linuxhomenetworking.com/wiki/index.php/Quick_HOWTO_:_Ch26_:_Linux_Software_RAID

http://www.planamente.ch/emidio/pages/linux_howto_root_lvm_raid_etch.php#5.1

mdadm -E /dev/hda1

root@pling:~# cat /etc/mdadm/mdadm.conf
# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=16a6ddf5:8afcf689:28c79ea4:d49b1739

# This file was auto-generated on Fri, 14 Mar 2008 15:25:28 -0700
# by mkconf $Id: mkconf 324 2007-05-05 18:49:44Z madduck $
root@pling:~#
root@pling:~#
root@pling:~# mdadm -E /dev/hda1
/dev/hda1:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : 16a6ddf5:8afcf689:28c79ea4:d49b1739
  Creation Time : Tue Jul  4 16:48:19 2006
     Raid Level : raid1
  Used Dev Size : 192643328 (183.72 GiB 197.27 GB)
     Array Size : 192643328 (183.72 GiB 197.27 GB)
   Raid Devices : 2
  Total Devices : 3
Preferred Minor : 0

    Update Time : Thu Mar 13 10:07:39 2008
          State : active
 Active Devices : 2
Working Devices : 2
 Failed Devices : 1
  Spare Devices : 0
       Checksum : e031b94b - correct
         Events : 0.42


      Number   Major   Minor   RaidDevice State
this     0       3        1        0      active sync   /dev/hda1

   0     0       3        1        0      active sync   /dev/hda1
   1     1       3       65        1      active sync   /dev/hdb1
root@pling:~# mdadm -E /dev/hdb1
/dev/hdb1:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : 16a6ddf5:8afcf689:28c79ea4:d49b1739
  Creation Time : Tue Jul  4 16:48:19 2006
     Raid Level : raid1
  Used Dev Size : 192643328 (183.72 GiB 197.27 GB)
     Array Size : 192643328 (183.72 GiB 197.27 GB)
   Raid Devices : 2
  Total Devices : 3
Preferred Minor : 0

    Update Time : Thu Mar 13 10:07:39 2008
          State : active
 Active Devices : 2
Working Devices : 2
 Failed Devices : 1
  Spare Devices : 0
       Checksum : e031b98d - correct
         Events : 0.42


      Number   Major   Minor   RaidDevice State
this     1       3       65        1      active sync   /dev/hdb1

   0     0       3        1        0      active sync   /dev/hda1
   1     1       3       65        1      active sync   /dev/hdb1
root@pling:~# lsmod | grep md
md_mod                 82324  1
amd74xx                15260  0 [permanent]
ide_core              116804  2 ide_disk,amd74xx
root@pling:~#
root@pling:~#

Just installing mdadm created the conf file.

The following make it work:

root@pling:~# modprobe md raid1 || modprobe md

root@pling:~# mdadm --assemble --scan

mdadm: /dev/md0 has been started with 2 drives.

root@pling:~# mkdir /brat
root@pling:~# mount -r /dev/md0 /brat
root@pling:~#
df /brat
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/md0             189620228  36042828 143945236  21% /brat
root@pling:~# ls /brat