[SLL] I can't find the start of my ext3 FS

[Darius Medhora]

Hi,
I have a situation where my 50G partition just refuses to mount or fsck.
I really don't want to loose the files on it so let me start by explaining
what happened.
I wiped out the first 512 bytes of the disk by mistake and therefore I 
lost the partition table of my disk.
I ran testdisk from knoppix to recreate the partitions however, testdisk
could not recreate 1 of them. This is the partition thats giving me 
problems. Can any one give me any solution to this please? Details of
disk follow:-

The partition I cannot mount or fsck is /dev/sda12

bash-3.00# fdisk -ls /dev/sda

Disk /dev/sda: 122.9 GB, 122942324736 bytes
16 heads, 63 sectors/track, 238216 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1       20318    10240240+  83  Linux
/dev/sda2           20319       30477     5120136   83  Linux
/dev/sda3           30478       40636     5120136   83  Linux
/dev/sda4           40637      196784    78698592    f  W95 Ext'd (LBA)
/dev/sda5           40637       44700     2048224+  83  Linux
/dev/sda6           44701       54388     4882720+  83  Linux
/dev/sda7           54389       56326      976720+  83  Linux
/dev/sda8           56327       57295      488344+  83  Linux
/dev/sda9           57296       61170     1952968+  82  Linux swap
/dev/sda10          61171       80546     9765472+  83  Linux
/dev/sda11          80547       99903     9755896+  83  Linux
/dev/sda12          99904      196784    48827992+  83  Linux

bash-3.00# fdisk -lu /dev/sda

Disk /dev/sda: 122.9 GB, 122942324736 bytes
16 heads, 63 sectors/track, 238216 cylinders, total 240121728 sectors
Units = sectors of 1 * 512 = 512 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63    20480543    10240240+  83  Linux
/dev/sda2        20480544    30720815     5120136   83  Linux
/dev/sda3        30720816    40961087     5120136   83  Linux
/dev/sda4        40961088   198358271    78698592    f  W95 Ext'd (LBA)
/dev/sda5        40961151    45057599     2048224+  83  Linux
/dev/sda6        45057663    54823103     4882720+  83  Linux
/dev/sda7        54823167    56776607      976720+  83  Linux
/dev/sda8        56776671    57753359      488344+  83  Linux
/dev/sda9        57753423    61659359     1952968+  82  Linux swap
/dev/sda10       61659423    81190367     9765472+  83  Linux
/dev/sda11       81190431   100702223     9755896+  83  Linux
/dev/sda12      100702287   198358271    48827992+  83  Linux
bash-3.00# 

bash-3.00# e2fsck /dev/sda12
e2fsck 1.38 (30-Jun-2005)
Couldn't find ext2 superblock, trying backup blocks...
e2fsck: Bad magic number in super-block while trying to open /dev/sda12

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>

bash-3.00# 
bash-3.00# mount /dev/sda12 /mnt
mount: you must specify the filesystem type
bash-3.00# 

A program i got from this great mailing list which displays the
blocks in the disk where superblocks may be found is as follows:
#!/usr/bin/python
'''
find_superblock.py

Finds possible superblocks in a drive, to aid with data recovery.

Usage:  find_superblock.py  /dev/hda

NOTE:  USE THIS AT YOUR OWN RISK!  NO WARRANTIES EXPRESSED OR IMPLIED.
Yada yada.  IANAL.  find_superblock.py must be run as root.  It does not
modify the contents of the drive in any way; but the information provided
by this program is not tested and may be very unreliable.
'''
import os, sys, struct

if len(sys.argv) != 2:
    print __doc__
    sys.exit()
f = open(sys.argv[1],'rb')
n = 1
while True:
    blk = f.read(512)
    if len(blk) == 0: break
    magic, volname = struct.unpack('56xH62x16s376x',blk)
    if magic == 0xef53:
        print '%d\t%s' % (n, volname)
    n += 1




However, I'm not sure if I should change the f.read to 4096 because
the block size of the filesystem could be 4096. If so, how do i do
that since I don't know python?

But a run of the same script gives this output:
bash-3.00# ./fsb.py /dev/sda12
19093
34549
34613
34725
40141
40245
40397
40629
40781
41037
41205
41429
42885
43021
43885
46901
etc etc etc etc...

BUT, if I try 19093

bash-3.00# e2fsck -b 19093 /dev/sda12
e2fsck 1.38 (30-Jun-2005)
e2fsck: Bad magic number in super-block while trying to open /dev/sda12

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>

bash-3.00# 

Can anyone please help me to fix this filesystem/partition?
I can do without all the other partitions/filesystems.

thanks!
d


      ____________________________________________________________________________________
Be a better sports nut!  Let your teams follow you 
with Yahoo Mobile. Try it now.  http://mobile.yahoo.com/sports;_ylt=At9_qDKvtAbMuh1G1SQtBI7ntAcJ