10-12-2011
First off, understand that modern hard drives ("modern" as in "last 15-25 years") have bad-sector remapping. When they spot a sector going bad, they take its contents and put it in a 'spare' location without telling you. So: your hard drive doesn't have a bad sector.
It has so many bad sectors that it's run out of spares. That could be a quarter of the drive or more, gone bad. This drive is not safe to use. Get your data off and stop using it before it betrays you.
You can't low-level format anymore. The densities they have these days, they only have the precision to do that at the factory. Dead sectors are dead for keeps.
A 'sector' is just a collection of zeroes and ones, there's not a magic combo of 512 bytes that makes a sector go bad. dd_rescue is safe. bad sectors can't be transferred. dd_rescue can't even read them, it fills in zeroes and skips.
Did you dd the entire disk, or just the partition?
Last edited by Corona688; 10-12-2011 at 07:35 PM..
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LEARN ABOUT NETBSD
badsect
BADSECT(8) BSD System Manager's Manual BADSECT(8)
NAME
badsect -- create files to contain bad sectors
SYNOPSIS
badsect bbdir sector ...
DESCRIPTION
badsect makes a file to contain a bad sector. Normally, bad sectors are made inaccessible by the standard formatter, which provides a for-
warding table for bad sectors to the driver; see bad144(8) for details. If a driver supports the bad blocking standard it is much preferable
to use that method to isolate bad blocks, since the bad block forwarding makes the pack appear perfect, and such packs can then be copied
with dd(1). The technique used by this program is also less general than bad block forwarding, as badsect can't make amends for bad blocks
in the i-list of file systems or in swap areas.
On some disks, adding a sector which is suddenly bad to the bad sector table currently requires the running of the standard DEC formatter.
Thus to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard badsect may be used to good
effect.
badsect is used on a quiet file system in the following way: First mount the file system, and change to its root directory. Make a directory
BAD there. Run badsect giving as argument the BAD directory followed by all the bad sectors you wish to add. The sector numbers must be
relative to the beginning of the file system, but this is not hard as the system reports relative sector numbers in its console error mes-
sages. Then change back to the root directory, unmount the file system and run fsck(8) on the file system. The bad sectors should show up
in two files or in the bad sector files and the free list. Have fsck(8) remove files containing the offending bad sectors, but do not have
it remove the BAD/nnnnn files. This will leave the bad sectors in only the BAD files.
badsect works by giving the specified sector numbers in a mknod(2) system call, creating an illegal file whose first block address is the
block containing bad sector and whose name is the bad sector number. When it is discovered by fsck(8) it will ask ``HOLD BAD BLOCK ?'' A
positive response will cause fsck(8) to convert the inode to a regular file containing the bad block.
DIAGNOSTICS
badsect refuses to attach a block that resides in a critical area or is out of range of the file system. A warning is issued if the block is
already in use.
SEE ALSO
bad144(8), fsck(8)
HISTORY
The badsect command appeared in 4.1BSD.
BUGS
If more than one of the sectors in a file system fragment are bad, you should specify only one of them to badsect, as the blocks in the bad
sector files actually cover all the sectors in a file system fragment.
BSD
June 5, 1993 BSD