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HELP! Rescuing an external HDD
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evoweiss
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Joined: 07 Sep 2003
Posts: 1532
Location: Edinburgh, Scotland

PostPosted: Tue Jul 15, 2014 11:37 pm    Post subject: Reply with quote

NeddySeagoon wrote:
USB HDD are slow, USB2 does not support DMA so the CPU has to read and write every byte.
USB to USB is even slower. USB3 is supposed to be better - it does DMA.


I'll say, though the wait is finally over.

Quote:
Show me some of the commands you hove been using and the resulting error messages in dmesg.


Here's a sampling. I went through the entire list you provided.

Code:
# mount -o ro,offset=32256,sb=102400000 /dev/sdd1 /mnt/image/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
# mount -o ro,offset=1048576,sb=102400000 /dev/sdd1 /mnt/image/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
# mount -o ro,offset=32256,sb=214990848 /dev/sdd1 /mnt/image/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.
# mount -o ro,offset=32256,sb=214990848 /dev/sdd1 /mnt/image/
mount: wrong fs type, bad option, bad superblock on /dev/loop0,
       missing codepage or helper program, or other error

       In some cases useful info is found in syslog - try
       dmesg | tail or so.


The dmesg output is

Code:

[952689.695228] UDF-fs: bad mount option "sb=102400000" or missing value
[952710.991317] EXT3-fs (loop0): error: unable to read superblock
[952710.991395] EXT2-fs (loop0): error: unable to read superblock
[952710.991464] EXT4-fs (loop0): unable to read superblock
[952710.991734] UDF-fs: bad mount option "sb=102400000" or missing value
[952728.361532] EXT3-fs (loop0): error: unable to read superblock
[952728.361630] EXT2-fs (loop0): error: unable to read superblock
[952728.361697] EXT4-fs (loop0): unable to read superblock
[952728.361962] UDF-fs: bad mount option "sb=214990848" or missing value
[952740.133372] EXT3-fs (loop0): error: unable to read superblock
[952740.133562] EXT2-fs (loop0): error: unable to read superblock
[952740.133704] EXT4-fs (loop0): unable to read superblock
[952740.134160] UDF-fs: bad mount option "sb=214990848" or missing value


Its possible that the root directory has been trashed. Thats why I was interested in the size of the file you incorrectly dd'ed.[/quote]

Thankfully, prior to crashing and burning I made sure to save the output indicating how much had been overwritten, etc.

Code:

dd if=/mnt/hdb1/Video/misc/linuxmint-16-xfce-dvd-32bit.iso of=/dev/sdc oflag=direct bs=1048576
dd: error writing ‘/dev/sdc’: Input/output error
26+0 records in
25+0 records out
26214400 bytes (26 MB) copied, 24.7105 s, 1.1 MB/s


So not very much, really.

Best,

Alex
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NeddySeagoon
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PostPosted: Wed Jul 16, 2014 5:27 pm    Post subject: Reply with quote

evoweiss,

Ahhh. The sb= parameter I provided is in units of of the filesystem (logical) block size. Thats 4k for your filesystem.
However, mount does not know the file system block size until its succeeded. That is too late for you.

Let me remind you
man nount:
         sb=n   Instead of block 1, use block n as  superblock.  This  could  be
              useful  when  the filesystem has been damaged.  (Earlier, copies
              of the superblock would be made every 8192 blocks: in  block  1,
              8193,  16385,  ...  (and  one  got  thousands of copies on a big
              filesystem).  Since  version  1.08,  mke2fs  has  a  -s  (sparse
              superblock)  option  to reduce the number of backup superblocks,
              and since version 1.15 this is the default. Note that  this  may
              mean  that ext2 filesystems created by a recent mke2fs cannot be
              mounted r/w under Linux 2.0.*.)  The block number here uses  1 k
              units.  Thus,  if  you  want  to  use  logical  block 32768 on a
              filesystem with 4 k blocks, use "sb=131072".


Notice the factor of 4 in
Code:
The block number here uses  1 k
              units.  Thus,  if  you  want  to  use  logical  block 32768 on a
              filesystem with 4 k blocks, use "sb=131072".


Your sb= parameters are out by a factor of 4.

With the first 26Mb gone, there is no point in trying alternate superblocks there.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
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evoweiss
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Joined: 07 Sep 2003
Posts: 1532
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PostPosted: Wed Jul 16, 2014 7:57 pm    Post subject: Reply with quote

Dear Neddy,

I take it to mean there's no hope then, right?

Is there any way to possibly rescue files from the drive?

Best,

Alex

NeddySeagoon wrote:
evoweiss,

Ahhh. The sb= parameter I provided is in units of of the filesystem (logical) block size. Thats 4k for your filesystem.
However, mount does not know the file system block size until its succeeded. That is too late for you.

Let me remind you
man nount:
         sb=n   Instead of block 1, use block n as  superblock.  This  could  be
              useful  when  the filesystem has been damaged.  (Earlier, copies
              of the superblock would be made every 8192 blocks: in  block  1,
              8193,  16385,  ...  (and  one  got  thousands of copies on a big
              filesystem).  Since  version  1.08,  mke2fs  has  a  -s  (sparse
              superblock)  option  to reduce the number of backup superblocks,
              and since version 1.15 this is the default. Note that  this  may
              mean  that ext2 filesystems created by a recent mke2fs cannot be
              mounted r/w under Linux 2.0.*.)  The block number here uses  1 k
              units.  Thus,  if  you  want  to  use  logical  block 32768 on a
              filesystem with 4 k blocks, use "sb=131072".


Notice the factor of 4 in
Code:
The block number here uses  1 k
              units.  Thus,  if  you  want  to  use  logical  block 32768 on a
              filesystem with 4 k blocks, use "sb=131072".


Your sb= parameters are out by a factor of 4.

With the first 26Mb gone, there is no point in trying alternate superblocks there.
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