• Overview:

  cat /proc/mdstat

• To view the status of an array:

  sudo mdadm --detail /dev/md0

• To mark a device as faulty:

  sudo mdadm /dev/md0 --set-faulty /dev/sda1

• To remove a failed or spare device:

  sudo mdadm /dev/md0 --remove /dev/sda1

• To add a device:

  sudo mdadm /dev/md0 --add /dev/sda1

Ubuntu server 10.04.1 installer has a known bug that prevents new installation on software RAID system from booting correctly (see http://ubuntuforums.org/showthread.php?t=1474950 for more details). One possible solution to get around this problem is to setup disk partition and software RAID using 9.10 installation CD before installing 10.04.

• HD: 500Gb * 3 (RAID 1, 1 hot spare)
  • /dev/md0: /boot, 200Mb, ext2
  • /dev/md1: /, 200Gb, ext4
  • /dev/md2: /var, 200Gb, ext4
  • /dev/md3: /home, 80Gb, ext4
  • /dev/md4: /tmp, 5Gb, ext4
  • /dev/md5: swap