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I saw similar questions, but didn't find what solution to my problem. After power-cut, one of RAID10 (4 disks were) appears to be malfunctioning. I make tha array active one, but can not mount it. Always the same error:

 mount: you must specify the filesystem type

So, here is what I have when type

  mdadm --detail /dev/md0

  /dev/md0:
    Version : 00.90.03
  Creation Time : Tue Sep  1 11:00:40 2009
   Raid Level : raid10
   Array Size : 1465148928 (1397.27 GiB 1500.31 GB)
  Used Dev Size : 732574464 (698.64 GiB 750.16 GB)
  Raid Devices : 4
  Total Devices : 3
  Preferred Minor : 0
   Persistence : Superblock is persistent

   Update Time : Mon Jun 11 09:54:27 2012
      State : clean, degraded
    Active Devices : 3
    Working Devices : 3
    Failed Devices : 0
    Spare Devices : 0

     Layout : near=2, far=1
 Chunk Size : 64K

       UUID : 1a02e789:c34377a1:2e29483d:f114274d
     Events : 0.166

Number   Major   Minor   RaidDevice State
   0       8       16        0      active sync   /dev/sdb
   1       0        0        1      removed
   2       8       48        2      active sync   /dev/sdd
   3       8       64        3      active sync   /dev/sde

At the /etc/mdadm/mdadm.conf I have

 by default, scan all partitions (/proc/partitions) for MD superblocks.
 alternatively, specify devices to scan, using wildcards if desired.
 DEVICE partitions

 auto-create devices with Debian standard permissions
 CREATE owner=root group=disk mode=0660 auto=yes

 automatically tag new arrays as belonging to the local system
 HOMEHOST <system>

 instruct the monitoring daemon where to send mail alerts
 MAILADDR root

  definitions of existing MD arrays
ARRAY /dev/md0 level=raid10 num-devices=4 UUID=1a02e789:c34377a1:2e29483d:f114274d
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=9b592be7:c6a2052f:2e29483d:f114274d

This file was auto-generated...

So, my question is, how can I mount md0 array (md1 has been mounted without problem) in order to preserve existing data? One more thing, fdisk -l command gives the following result:

 Disk /dev/sdb: 750.1 GB, 750156374016 bytes
 255 heads, 63 sectors/track, 91201 cylinders
 Units = cylinders of 16065 * 512 = 8225280 bytes
 Disk identifier: 0x660a6799

 Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1       88217   708603021   83  Linux
/dev/sdb2           88218       91201    23968980    5  Extended
/dev/sdb5           88218       91201    23968948+  82  Linux swap / Solaris

Disk /dev/sdc: 750.1 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x0008f8ae

 Device Boot      Start         End      Blocks   Id  System
 /dev/sdc1               1       88217   708603021   83  Linux
 /dev/sdc2           88218       91201    23968980    5  Extended
 /dev/sdc5           88218       91201    23968948+  82  Linux swap / Solaris

 Disk /dev/sdd: 750.1 GB, 750156374016 bytes
 255 heads, 63 sectors/track, 91201 cylinders
 Units = cylinders of 16065 * 512 = 8225280 bytes
 Disk identifier: 0x4be1abdb

  Device Boot      Start         End      Blocks   Id  System

  Disk /dev/sde: 750.1 GB, 750156374016 bytes
  255 heads, 63 sectors/track, 91201 cylinders
  Units = cylinders of 16065 * 512 = 8225280 bytes
  Disk identifier: 0xa4d5632e

  Device Boot      Start         End      Blocks   Id  System

  Disk /dev/sdf: 750.1 GB, 750156374016 bytes
  255 heads, 63 sectors/track, 91201 cylinders
  Units = cylinders of 16065 * 512 = 8225280 bytes
  Disk identifier: 0xdacb141c

  Device Boot      Start         End      Blocks   Id  System

  Disk /dev/sdg: 750.1 GB, 750156374016 bytes
  255 heads, 63 sectors/track, 91201 cylinders
  Units = cylinders of 16065 * 512 = 8225280 bytes
  Disk identifier: 0xdacb141c

  Device Boot      Start         End      Blocks   Id  System

  Disk /dev/md1: 750.1 GB, 750156251136 bytes
  2 heads, 4 sectors/track, 183143616 cylinders
  Units = cylinders of 8 * 512 = 4096 bytes
  Disk identifier: 0xdacb141c

  Device Boot      Start         End      Blocks   Id  System
  Warning: ignoring extra data in partition table 5
  Warning: ignoring extra data in partition table 5
  Warning: ignoring extra data in partition table 5
  Warning: invalid flag 0x7b6e of partition table 5 will be corrected by w(rite)

  Disk /dev/md0: 1500.3 GB, 1500312502272 bytes
  255 heads, 63 sectors/track, 182402 cylinders
  Units = cylinders of 16065 * 512 = 8225280 bytes
  Disk identifier: 0x660a6799

   Device Boot      Start         End      Blocks   Id  System
  /dev/md0p1   *           1       88217   708603021   83  Linux
  /dev/md0p2           88218       91201    23968980    5  Extended
  /dev/md0p5   ?      121767      155317   269488144   20  Unknown

And one more thing. When using mdadm --examine command, here ise result:

 mdadm -v --examine --scan /dev/sdb /dev/sdc /dev/sdd /dev/sde /dev/sdf /dev/sd
 ARRAY /dev/md1 level=raid1 num-devices=2 UUID=9b592be7:c6a2052f:2e29483d:f114274d
  devices=/dev/sdf

 ARRAY /dev/md0 level=raid10 num-devices=4 UUID=1a02e789:c34377a1:2e29483d:f114274d
 devices=/dev/sdb,/dev/sdc,/dev/sdd,/dev/sde

md0 has 3 devices which are active. Can someone instruct me how to solve this issue? If it is possible, I would like not to removing faulty HDD. Please advise

share|improve this question
    
It's a mess. What is layout of your disks and RAIDs, don't you know? –  poige Jun 11 '12 at 10:18
    
What do you mean by "layout". –  Zoran Jun 11 '12 at 11:17

1 Answer 1

up vote 1 down vote accepted

You are dealing with a loss of raid superblock, you will need to stop the array, to remove it, to zerosuperblog the member devices and then to rebuild your array.

Two critical informations have to be correct when rebuilding the array :

  • the devices order
  • the chunk size

You can refer to this wiki that describes how to Recover from a loss of raid superblock for a detailed procedure

share|improve this answer
    
"You are dealing with a loss of raid superblock" — does your crystal ball say so? –  poige Jun 11 '12 at 10:11
    
I will try that, but before could you please tell me I am loose the valuable data on array or not? Again, I will thank you when I try that –  Zoran Jun 11 '12 at 10:54
    
@zoran In your case, there is only one failed device, so you can safely rebuild your array –  m0ntassar Jun 11 '12 at 11:57
    
Thank you very much. I will do that –  Zoran Jun 11 '12 at 12:07
    
@m0ntassar. Another problem appeared /dev/sdc is busy so I can not zero it. Is there another solution except dd (deleting whole disk)? Please advise –  Zoran Jun 13 '12 at 8:24

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