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I have two identical 3 TB disks that were in a RAID1 array, where one disk crashed. I replaced the failed disk, but not after the RAID partitions got messed up.

I need to figure out how to restore the RAID array and get at my ext4 partition.

State of the surviving disk

Here are the properties of the surviving disk:

# fdisk -l /dev/sda

fdisk: device has more than 2^32 sectors, can't use all of them

Disk /dev/sda: 2199.0 GB, 2199023255040 bytes
255 heads, 63 sectors/track, 267349 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks  Id System
/dev/sda1               1      267350  2147483647+ ee EFI GPT

# parted /dev/sda print

Model: ATA ST3000DM001-9YN1 (scsi)
Disk /dev/sda: 3001GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name  Flags
 1      131kB   2550MB  2550MB  ext4                  raid
 2      2550MB  4698MB  2147MB  linux-swap(v1)        raid
 5      4840MB  3001GB  2996GB                        raid

I replaced the failed drive, and cloned the surviving drive to it so I have something to work with. I cloned the drives with dd if=/dev/sdb of=/dev/sda conv=noerror bs=64M, and now /dev/sda and /dev/sdb are identical.

Here is the RAID information:

# cat /proc/mdstat

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] 
md1 : active raid1 sdb2[1]
      2097088 blocks [2/1] [_U]

md0 : active raid1 sdb1[1]
      2490176 blocks [2/1] [_U]

unused devices: <none>

It seems that md2 is missing.

What TestDisk tells me

Here is what testdisk 6.14-WIP finds on the surviving disk:

Disk /dev/sda - 3000 GB / 2794 GiB - CHS 364801 255 63
Current partition structure:
     Partition                  Start        End    Size in sectors

 1 P Linux Raid                   256    4980735    4980480 [md0]
 2 P Linux Raid               4980736    9175039    4194304 [md1]
Invalid RAID superblock
 5 P Linux Raid               9453280 5860519007 5851065728
 5 P Linux Raid               9453280 5860519007 5851065728

# After a quick search
Disk /dev/sda - 3000 GB / 2794 GiB - CHS 364801 255 63
     Partition               Start        End    Size in sectors
 D MS Data                      256    4980607    4980352 [1.41.12-2197]
 D Linux Raid                   256    4980735    4980480 [md0]
 D Linux Swap               4980736    9174895    4194160
 D Linux Raid               4980736    9175039    4194304 [md1]
>P MS Data                  9481056 5858437983 5848956928 [1.41.12-2228]

And listing the files on the last partition in the list shows all of my files intact.

Here is what testdisk 6.14-WIP finds on the failed disk:

Disk /dev/sda - 3000 GB / 2794 GiB - CHS 364801 255 63
Current partition structure:
     Partition                  Start        End    Size in sectors

 1 P Linux Raid                   256    4980735    4980480 [md0]
 2 P Linux Raid               4980736    9175039    4194304 [md1]
 5 P Linux Raid               9453280 5860519007 5851065728 [DiskStation:2]

# After a quicksearch
Disk /dev/sda - 3000 GB / 2794 GiB - CHS 364801 255 63
     Partition               Start        End    Size in sectors
>D MS Data                      256    4980607    4980352 [1.41.12-2197]
 D Linux Raid                   256    4980735    4980480 [md0]
 D Linux Swap               4980736    9174895    4194160
 D Linux Raid               4980736    9175039    4194304 [md1]
 P Linux Raid               9453280 5860516583 5851063304 [DiskStation:2]

Here is what testdisk 6.14-WIP finds on the raid devices:

Disk /dev/md0 - 2549 MB / 2431 MiB - CHS 622544 2 4
Current partition structure:
     Partition                  Start        End    Size in sectors

   P ext4                     0   0  1 622543   1  4    4980352 [1.41.12-2197]

Disk /dev/md1 - 2147 MB / 2047 MiB - CHS 524272 2 4
Current partition structure:
     Partition                  Start        End    Size in sectors

   P Linux SWAP 2             0   0  1 524271   1  4    4194176

Recreating the RAID1 array

Update: I re-created the RAID1 array with just one disk, but the partitions won't mount.

# mdadm --create /dev/md2 --metadata=1.2 --verbose --level=mirror --raid-devices=2 missing /dev/sdb5

mdadm: size set to 2925531648K
mdadm: array /dev/md2 started.

# cat /proc/mdstat

Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] 
md2 : active raid1 sdb5[1]
      2925531648 blocks super 1.2 [2/1] [_U]

md1 : active raid1 sdb2[1]
      2097088 blocks [2/1] [_U]

md0 : active raid1 sdb1[1]
      2490176 blocks [2/1] [_U]

unused devices: <none>

# parted /dev/md2 print

Error: /dev/md2: unrecognised disk label
Model: Linux Software RAID Array (md)                                     
Disk /dev/md2: 2996GB
Sector size (logical/physical): 512B/512B
Partition Table: unknown
Disk Flags: 

# parted /dev/sdb5 print

Error: /dev/sdb5: unrecognised disk label
Model: Unknown (unknown)                                                  
Disk /dev/sdb5: 2996GB
Sector size (logical/physical): 512B/512B
Partition Table: unknown
Disk Flags: 

# mdadm --detail /dev/md2

/dev/md2:
        Version : 1.2
  Creation Time : Wed Dec  5 22:58:38 2012
     Raid Level : raid1
     Array Size : 2925531648 (2790.00 GiB 2995.74 GB)
  Used Dev Size : 2925531648 (2790.00 GiB 2995.74 GB)
   Raid Devices : 2
  Total Devices : 1
    Persistence : Superblock is persistent

    Update Time : Thu Dec  6 00:10:43 2012
          State : clean, degraded
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

           Name : DiskStation:2  (local to host DiskStation)
           UUID : ccd2b669:fbd73c43:3c84590d:74bff584
         Events : 6

    Number   Major   Minor   RaidDevice State
       0       0        0        0      removed
       1       8       21        1      active sync   /dev/sdb5

# mdadm --examine /dev/sdb5

/dev/sdb5:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : ccd2b669:fbd73c43:3c84590d:74bff584
           Name : DiskStation:2  (local to host DiskStation)
  Creation Time : Wed Dec  5 22:58:38 2012
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 5851063680 (2790.00 GiB 2995.74 GB)
     Array Size : 5851063296 (2790.00 GiB 2995.74 GB)
  Used Dev Size : 5851063296 (2790.00 GiB 2995.74 GB)
    Data Offset : 2048 sectors
   Super Offset : 8 sectors
          State : clean
    Device UUID : 234e84ca:1b65842b:6cd51fb9:521727ae

    Update Time : Thu Dec  6 00:46:24 2012
       Checksum : bb03c6da - correct
         Events : 8


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

Failing to mount the array

# mount /dev/md2 /mnt/md2

mount: mounting /dev/md2 on /mnt/md2 failed: No such device

# mount /dev/sdb5 /mnt/sdb5

mount: mounting /dev/sdb5 on /mnt/sdb5 failed: No such device
share|improve this question
    
Have you tried running fsck.ext4 against the failed partition? –  Simplexion Dec 5 '12 at 5:46
    
I can't even access the '/dev/sda5' device because it has a bad superblock. –  Neil Dec 5 '12 at 9:42
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