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Re: recover data from linear raid




I managed to get the hard disk of the retired system and this is its raid-related boot log:

md: Autodetecting RAID arrays.
 [events: 0000004d]
 [events: 0000004d]
md: autorun ...
md: considering hdb1 ...
md:  adding hdb1 ...
md:  adding hdc1 ...
md: created md0
md: bind<hdc1,1>
md: bind<hdb1,2>
md: running: <hdb1><hdc1>
md: hdb1's event counter: 0000004d
md: hdc1's event counter: 0000004d
md0: max total readahead window set to 512k
md0: 2 data-disks, max readahead per data-disk: 256k
raid0: looking at hdb1
raid0:   comparing hdb1(244195904) with hdb1(244195904)
raid0:   END
raid0:   ==> UNIQUE
raid0: 1 zones
raid0: looking at hdc1
raid0:   comparing hdc1(293049600) with hdb1(244195904)
raid0:   NOT EQUAL
raid0:   comparing hdc1(293049600) with hdc1(293049600)
raid0:   END
raid0:   ==> UNIQUE
raid0: 2 zones
raid0: FINAL 2 zones
raid0: zone 0
raid0: checking hdb1 ... contained as device 0
  (244195904) is smallest!.
raid0: checking hdc1 ... contained as device 1
raid0: zone->nb_dev: 2, size: 488391808
raid0: current zone offset: 244195904
raid0: zone 1
raid0: checking hdb1 ... nope.
raid0: checking hdc1 ... contained as device 0
  (293049600) is smallest!.
raid0: zone->nb_dev: 1, size: 48853696
raid0: current zone offset: 293049600
raid0: done.
raid0 : md_size is 537245504 blocks.
raid0 : conf->smallest->size is 48853696 blocks.
raid0 : nb_zone is 11.
raid0 : Allocating 88 bytes for hash.
md: ... autorun DONE.



As Christian said, specific error message help a lot.
Assume the two devices are hdc and hde,

 fdisk -l /dev/hdc
 fdisk -l /dev/hde
 mdadm -E /dev/hdc
 mdadm -E /dev/hde

and my best guess

  mdadm --build /dev/md0 --level linear --raid-disks 2 /dev/hdc /dev/hde
  fsck -n /dev/md0

(and linux-raid vger kernel org might be a better mailing list for
this particular sort of problem).

Disk /dev/hdb: 250.0 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

  Device Boot    Start       End    Blocks   Id  System
[root node004 root]# fdisk -l /dev/hdc

Disk /dev/hdc: 300.0 GB, 300090728448 bytes
255 heads, 63 sectors/track, 36483 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

  Device Boot    Start       End    Blocks   Id  System
[root node004 root]# mdadm -E /dev/hdb
/dev/hdb:
         Magic : a92b4efc
       Version : 00.90.00
          UUID : 293be3e8:5a7ac6e7:adefc469:84f8aefb
 Creation Time : Fri Jun 23 15:47:10 2006
    Raid Level : linear
   Device Size : 244198464 (232.89 GiB 250.06 GB)
  Raid Devices : 2
 Total Devices : 2
Preferred Minor : 0

   Update Time : Fri Jun 23 15:48:43 2006
         State : clean, no-errors
Active Devices : 2
Working Devices : 2
Failed Devices : 0
 Spare Devices : 0
      Checksum : f790e07f - correct
        Events : 0.2

      Rounding : 32K

     Number   Major   Minor   RaidDevice State
this     0       3       64        0      active sync   /dev/hdb
  0     0       3       64        0      active sync   /dev/hdb
  1     1      22        0        1      active sync   /dev/hdc
[root node004 root]# mdadm -E /dev/hdc
/dev/hdc:
         Magic : a92b4efc
       Version : 00.90.00
          UUID : 293be3e8:5a7ac6e7:adefc469:84f8aefb
 Creation Time : Fri Jun 23 15:47:10 2006
    Raid Level : linear
   Device Size : 244198464 (232.89 GiB 250.06 GB)
  Raid Devices : 2
 Total Devices : 2
Preferred Minor : 0

   Update Time : Fri Jun 23 15:48:43 2006
         State : clean, no-errors
Active Devices : 2
Working Devices : 2
Failed Devices : 0
 Spare Devices : 0
      Checksum : f790e054 - correct
        Events : 0.2

      Rounding : 32K

     Number   Major   Minor   RaidDevice State
this     1      22        0        1      active sync   /dev/hdc
  0     0       3       64        0      active sync   /dev/hdb
  1     1      22        0        1      active sync   /dev/hdc
[root node004 root]# mdadm --build /dev/md0 --level linear --raid-disks 2 /dev/hdb /dev/hdc
mdadm: array /dev/md0 built and started.

fsck -n /dev/md0
fsck 1.32 (09-Nov-2002)
e2fsck 1.32 (09-Nov-2002)
Couldn't find ext2 superblock, trying backup blocks...
fsck.ext2: Bad magic number in super-block while trying to open /dev/md0

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
   e2fsck -b 8193 <device>

fsck -b 8193 /dev/md0
fsck 1.32 (09-Nov-2002)
e2fsck 1.32 (09-Nov-2002)
fsck.ext2: Bad magic number in super-block while trying to open /dev/md0

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
   e2fsck -b 8193 <device>


During a recovery attemp today by mistake I created a mirror array with hdb as the primary and hdc as the secondary. I interrupted the array creation almost immediately, but part of the hdc was overwritten. However the array never held more than 70 gbytes of data, so I hope everything is intact on hdb :/


	Thank you all for your kind help:)
--
============================================================================

Dimitris Zilaskos

Department of Physics @ Aristotle University of Thessaloniki , Greece
PGP key : http://tassadar.physics.auth.gr/~dzila/pgp_public_key.asc
	  http://egnatia.ee.auth.gr/~dzila/pgp_public_key.asc
MD5sum  : de2bd8f73d545f0e4caf3096894ad83f  pgp_public_key.asc
============================================================================

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