HOWTO: recover data from RAID1

Scenario: two or more HDs configured as RAID1. One of them gets broken and the computer doesn’t boot for any reason.
Problem: access data in the partition to recover them. It is not possible to mount it directly because it is a RAID partition, so:

1. Create an image of the good disk using dd and secure it
2. Take another pc with debian/ubuntu (or similar distro)
3. Using an usb<->sata adapter, plug the disk in the new computer and make note of the device checking the output using dmesg (eg. /dev/sdc)
4. Verify with fdisk/cfdisk the partition table of the disk: there should be one or more raid autodetect partitions

5. Open a terminal and type

   $ mdadm --assemble --run /dev/md0 /dev/sdc1
   

   to create a temporary RAID1 and to make it available using /dev/md0

6. If it doesn’t work, maybe the RAID kernel module is not loaded.

   $ modprobe raid1
   

   and try again

7. If everything is OK, it will be possible to mount /dev/md0:

   $ mount /dev/md0 /mnt
   

8. If the above command gives back invalid argument, likely the ext3 module is not loaded.

   $ modprobe ext3
   

   and try again

9. If mount hasn’t given back any error, it will be possible to mount to access data in the raid1 from /mnt
10. Save all you can save
11. Umount /mnt

12. Stop the temporary raid1 using

    $ mdadm --stop /dev/md0
    

13. If necessary, repeat the same process with the other partitions

    $ mdadm --assemble --run /dev/md1 /dev/sdc2
    

14. Done

WARNING: if you have a RAID5, this procedure won’t work.

Many thanks to Lorenzo