Detecting RAID partitions using Ubuntu Live CD or USB

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If one of the disks on Ubuntu software RAID installation fails then system may fail to boot. In such cases one can boot using Ubuntu Live CD or USB and detect RAID partitions using following steps:

  1. Install mdadm using 'apt-get -y install mdadm'. Ignore errors related to /etc/fstab shown during installation.
  2. If LVM was used on top of RAID then use 'apt-get -y install lvm2' to install lvm. In such cases after RAID partitions are detected one may need to activate lvm volume groups using 'vgchange -a y'
  3. Try 'more /proc/mdstat' to see if RAID arrays have been detected.
  4. If 'more /proc/mdstat' output is empty, then try to detect arrays using 'mdadm --auto-detect'. Test again with 'more /proc/mdstat' to check if arrays are detected.
  5. If arrays are not detected even now use
    apt-get -y install dmraid
    modprobe dm_mod
    dmraid -ay
    If apt-gives duplicate sources error for cdrom then edit /etc/apt/sources.list and remove lines related to cdrom. It is advisable to copy sources.list to sources.list2 before deleting cdrom as package source.
  6. If 'more /proc/mdstat' output is still empty, then try to detect arrays using 'mdadm --auto-detect'. Test again with 'more /proc/mdstat' to check if arrays are detected.
  7. If arrays are detected and inactive (S) then they can be activated without redundancy using 'mdadm --run /dev/md<n>' where <n> can be replaced with appropriate raid device number as shown in 'more /proc/mdstat' output.
  8. Once arrays are active corresponding raid partition devices would be available in '/dev/mapper'. They can be mounted using mount as normal partitions.




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