Greg,

You don't really need to use hdparm. You can use dd to overwrite the
bad sectors with zeros which forces the disk to remap the sector.

As for calculating the new data, a friend of mine wrote me a java
program that takes in any number of input files and XORs them, then
writes the output to a file.
The input files are the sectors' data from other disks.

I have attached the program in case any one is interested. Courtesy to
Eng. Hisham Farahat who wrote the program "sector xor, or sexor, as I
call it"

java -jar sexor.jar file1 file2 ... fileN

The output file will always be called "out" -- do not include it in
the input list.

On Fri, Sep 18, 2009 at 9:02 PM, Greg Freemyer [off-list ref] wrote:

All,

I keep forgetting to ask, but the subject of this thread makes me
wonder if you guys are familiar with the hdparm features of
"--make-bad-sector", "--read-sector", and "--write-sector".

I don't know if any of those can be used to force a sector to be
remapped, but I could see a user space process like:

identify corrupt sector
hdparm --make-bad-sector   (to get it as corrupt as linux knows how).
calculate correct value
write new value to sector the normal way (hopefully the drive will
remap the bad sector)

hdparm --read-sector will do a low level read of the sector, including
the sector header and checksum as I understand it.  I'm not sure all
that gets back to userspace.

hdparm --write-sector will force a sector to be rewritten.  I don't
believe it is meant to ever cause a sector remap.  Of course you never
know what a disk drive is going to do for any given command.

Mark Lord is of course the expert on all things hdparm.

Greg
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