====== RAID - mdadm - Troubleshooting - No md superblock detected ======

The error is seen when examining the disk.

<code bash>
mdadm --examine /dev/sdb
</code>

returns:

<code bash>
mdadm: No md superblock detected on /dev/sdb
</code>

----

===== Check if there is at least one intact superblock within the RAID Array =====

Check the other disks within the RAID Array:

<code bash>
mdadm --examine /dev/sde
</code>

returns:

<code bash>
/dev/sde:
          Magic : a92b4efc
        Version : 00.90.00
           UUID : f781ba39:3975fa64:c36d41f1:ea056919
  Creation Time : Mon Jan  5 14:18:27 2009
     Raid Level : raid5
  Used Dev Size : 976762496 (931.51 GiB 1000.20 GB)
     Array Size : 2930287488 (2794.54 GiB 3000.61 GB)
   Raid Devices : 4
  Total Devices : 4
Preferred Minor : 0

    Update Time : Thu Mar 19 22:39:52 2009
          State : clean
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0
       Checksum : 54f44664 - correct
         Events : 0.92

         Layout : left-symmetric
     Chunk Size : 64K

      Number   Major   Minor   RaidDevice State
this     3       8       32        3      active sync   /dev/sdc

   0     0       8       16        0      active sync   /dev/sdb
   1     1       8       64        1      active sync   /dev/sde
   2     2       8       48        2      active sync   /dev/sdd
   3     3       8       32        3      active sync   /dev/sdc
</code>

----

===== Stop the RAID Array =====

<code bash>
mdadm --stop /dev/md0
</code>

returns:

<code bash>
mdadm: stopped /dev/md0
</code>

----

===== Try to Assemble the RAID Array =====

<code bash>
mdadm --assemble --scan -v
</code>

returns:

<code bash>
mdadm: /dev/sde1 is identified as a member of /dev/md0, slot 2.
mdadm: /dev/sdf1 is identified as a member of /dev/md0, slot 3.
mdadm: /dev/sdd1 is identified as a member of /dev/md0, slot 0.
mdadm: /dev/sdb1 is identified as a member of /dev/md0, slot 1.
mdadm: added /dev/sdd1 to /dev/md0 as 0 (possibly out of date)
mdadm: added /dev/sdb1 to /dev/md0 as 1 (possibly out of date)
mdadm: added /dev/sdf1 to /dev/md0 as 3 (possibly out of date)
mdadm: added /dev/sde1 to /dev/md0 as 2
mdadm: /dev/md0 assembled from 1 drive - not enough to start the array.
</code>

<WRAP info>
**NOTE:**  The last message shows this cannot assemble the RAID Array with only the one drive.
</WRAP>

----

===== Force a Reassemble =====

If the previous command fails, try to repeat the assemble with the **--run** or **--force** options: <code bash>
mdadm --assemble --scan -v --force
</code>

or 

<code bash>
mdadm --assemble --scan -v --run
</code>

<WRAP important>
**WARNING:**  These options may destroy your data!
</WRAP>

----

===== Recreate the RAID Array =====

If the Array is still not working, try to recreate the array:

<code bash>
mdadm create /dev/md0 --assume-clean <original create options> /dev/sd[dbfe]1.
</code>

<WRAP important>
**WARNING:**  All of these options may destroy your data.
</WRAP>

----

===== References =====

https://ahelpme.com/linux/inactive-array-mdadm-cannot-get-array-info-for-dev-md126/

https://www.linuxquestions.org/questions/linux-general-1/recovering-mdadm-superblocks-713234/