[ale] Fwd: Hard Drive Death Spiral -- AKA Recovery Software?

[Ed Cashin]

On Thu, Dec 11, 2008 at 10:54 AM, H P Ladds <householdwords at gmail.com> wrote:
> Hey All,
>
> I have a hard drive that appears to be dieing, and I need data
> recovery software. Any suggestions?
...
> 5. I guess what I need to do is reformat the drive without destroying
> the data on the disk, which is mostly impossible -- right?

If the hard drive is dying, then you can copy the bytes off of
it now before it dies and sort out the structure of the data later.

When I had a dying hard drive it would not allow reads from
a bunch of sectors.  I read its contents to files in 100 MB chunks.
For each chunk where there was an error, I read 1 MB chunks,
for each 1 MB chunk where an error occurred, I read 8 KB chunks.
At that point I decided to stop, because the read errors took a
while to manifest, and the recovery was getting slow.

Because each of the chunk files was named by its offset into
the disk, I could then seek in a sparse file and write the data
to the correct position (being careful not to truncate the sparse
file).

The whole process took a whole weekend, but it is the most
conservative way I can imagine to recover data from a dying
drive.  If you aren't having read errors, all of the 100 MB files
would read successfully, and you'd be able to just cat them
together without any sparse file shenanigans.

-- 
  Ed Cashin <ecashin at noserose.net>