Rubin Shrestha
Rubin Shrestha
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Can’t assemble RAID 6 with 1 faulty disk

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A RAID 6 array on a old NAS (LaCie 5big Network 2) of mine lost a disk (it’s dead) and stopped booting (I let it try a few hours with and without the faulty disk before shutting it down, because I know that a rebuild can be long).

It’s RAID 6 array with 5 disks and one of them is marked as spare but is used in the RAID for years it seems (since the last drive death) so I should not have any data loss.

As the NAS uses standard mdadm + XFS, I tried to reassemble it in an old desktop (with systemrescue on a stick) in which I plug the 4 working disks (I can only plug 4 ATM). --assemble --scan didn’t worked. The -E --scan does create a config file with the correct Array UUID :

ARRAY /dev/md/4  metadata=1.0 UUID=cb13911d:63bddb27:90f2c9ea:6652f584
   spares=1

but when I try to assemble, it gives me the following error :

root@localhost# mdadm --assemble /dev/md/4 
mdadm: device 10 in /dev/md/4 has wrong state in superblock, but /dev/sdj2 seems ok
mdadm: /dev/md/4 assembled from 1 drive and 1 spare - not enough to start the array.

The -E on every partition is a bit weird as “Array state” and “Events” differs but the other entry seems correct. I lack of understandings to know how I can fix this. Do any of you have an idea on how I can reassemble the RAID (with one missing disk for now, until I can find reliable hardware to finish rebuilding a safe RAID) ?

--examine for raid members :

/dev/sda2:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : cb13911d:63bddb27:90f2c9ea:6652f584
           Name : (none):4
  Creation Time : Mon Jan  4 07:29:11 2010
     Raid Level : raid6
   Raid Devices : 5

 Avail Dev Size : 7809984512 sectors (3.64 TiB 4.00 TB)
     Array Size : 11714976768 KiB (10.91 TiB 12.00 TB)
   Super Offset : 7809984768 sectors
   Unused Space : before=0 sectors, after=256 sectors
          State : clean
    Device UUID : c6c7a7c4:93070172:f3e016ac:4fd3974b

    Update Time : Thu Jun  5 21:28:26 2025
       Checksum : 579f23f6 - correct
         Events : 3883067

         Layout : left-symmetric-6
     Chunk Size : 512K

   Device Role : Active device 0
   Array State : A.AAA ('A' == active, '.' == missing, 'R' == replacing)


/dev/sdb2:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : cb13911d:63bddb27:90f2c9ea:6652f584
           Name : (none):4
  Creation Time : Mon Jan  4 07:29:11 2010
     Raid Level : raid6
   Raid Devices : 5

 Avail Dev Size : 7809984512 sectors (3.64 TiB 4.00 TB)
     Array Size : 11714976768 KiB (10.91 TiB 12.00 TB)
   Super Offset : 7809984768 sectors
   Unused Space : before=0 sectors, after=256 sectors
          State : clean
    Device UUID : dd4fa94d:6a8146f2:3a75654d:82517cc3

    Update Time : Thu Jun  5 21:34:30 2025
       Checksum : 7a1939c8 - correct
         Events : 3883071

         Layout : left-symmetric-6
     Chunk Size : 512K

   Device Role : Active device 2
   Array State : ..A.. ('A' == active, '.' == missing, 'R' == replacing)


/dev/sdi2:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : cb13911d:63bddb27:90f2c9ea:6652f584
           Name : (none):4
  Creation Time : Mon Jan  4 07:29:11 2010
     Raid Level : raid6
   Raid Devices : 5

 Avail Dev Size : 7809984512 sectors (3.64 TiB 4.00 TB)
     Array Size : 11714976768 KiB (10.91 TiB 12.00 TB)
   Super Offset : 7809984768 sectors
   Unused Space : before=0 sectors, after=256 sectors
          State : clean
    Device UUID : 6e04ad75:2be2a49b:fcaa8337:caeb6237

    Update Time : Thu Jun  5 21:31:27 2025
       Checksum : a97f1e6b - correct
         Events : 3883068

         Layout : left-symmetric-6
     Chunk Size : 512K

   Device Role : Active device 3
   Array State : ..AA. ('A' == active, '.' == missing, 'R' == replacing)


/dev/sdj2:
          Magic : a92b4efc
        Version : 1.0
    Feature Map : 0x0
     Array UUID : cb13911d:63bddb27:90f2c9ea:6652f584
           Name : (none):4
  Creation Time : Mon Jan  4 07:29:11 2010
     Raid Level : raid6
   Raid Devices : 5

 Avail Dev Size : 7809984512 sectors (3.64 TiB 4.00 TB)
     Array Size : 11714976768 KiB (10.91 TiB 12.00 TB)
   Super Offset : 7809984768 sectors
   Unused Space : before=0 sectors, after=256 sectors
          State : clean
    Device UUID : 91423e8a:28b01f4a:dd053669:cc2d7beb

    Update Time : Thu Jun  5 18:25:58 2025
       Checksum : 52579bf8 - correct
         Events : 3883064

         Layout : left-symmetric-6
     Chunk Size : 512K

   Device Role : spare
   Array State : A.AAA ('A' == active, '.' == missing, 'R' == replacing)

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