Mounting Software RAID1 member: madadm

(1)I connected my old hard drive and realized that it was RAID member:



#fdisk -l /dev/sdd
Disk /dev/sdd: 250.1 GB, 250058268160 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488395055 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x90909090

   Device Boot      Start         End      Blocks   Id  System
/dev/sdd1   *        2048     2099199     1048576   fd  Linux raid autodetect
/dev/sdd2         2099200     6293503     2097152   82  Linux swap / Solaris
/dev/sdd3         6293504    69208063    31457280   fd  Linux raid autodetect
/dev/sdd4        69208064   488394751   209593344   fd  Linux raid autodetect

You cannot mount it as a normal partition

#mkdir /mnt/old_hdd 

#mount /dev/sdd4 /mnt/old_hdd 

mount: unknown filesystem type 'linux_raid_member'

(2) If you are using RAID1 array, you can mount using madadm

#mdadm --examine /dev/sdd4

/dev/sdd4:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : 957e7cb5:bfd41f70:9cb84b0d:f53e5a4c
           Name : milosz-desktop:2
  Creation Time : Sat Aug 20 18:48:26 2011
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 419184640 (199.88 GiB 214.62 GB)
     Array Size : 419184496 (199.88 GiB 214.62 GB)
  Used Dev Size : 419184496 (199.88 GiB 214.62 GB)
    Data Offset : 2048 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : db8a694f:750a0ded:22a6d046:5c4db280

    Update Time : Tue May  8 20:50:32 2012
       Checksum : 75dbc3b6 - correct
         Events : 191


   Device Role : Active device 1
   Array State : .A ('A' == active, '.' == missing)


In order to mount it properly, you will have to create a md virtual device with mdadm.

#mdadm -A -R /dev/md9 /dev/sdd4

mdadm: /dev/md9 has been started with 1 drive (out of 2).

Now you can mount /dev/md9 without any problem.

#mount /dev/md9 /mnt/old_hdd/

#mount | grep ^/dev/md9

/dev/md9 on /mnt/old_hdd type ext4 (rw)

You will be able to copy the data to another drive now. Once the data is transferred, you can unmount it as follows 

#umount /mnt/old_hdd 

#mdadm -S /dev/md9

mdadm: stopped /dev/md9