[kwlug-disc] Media errors on a USB disk
John Van Ostrand
john at netdirect.ca
Sun Oct 24 11:23:48 EDT 2010
----- Original Message -----
> A disk diagnostic program should just be reading the raw sectors of
> data. Is the sector readable? If not, is it recoverable? If not, can
> the drive firmware re-map that sector to a spare?
> How an OS organizes the data shouldn't make any difference to a
> hardware-level diagnostic program. It shouldn't care about partition
> tables or partitions, file system, or empty space.
> Disk diagnostics are different from file system diagnostics, like fsck
> or chkdsk. File system diagnostics can only check their own kind of
> file system, only within that partition. There's no ability to use the
> hardware sector remapping (but the file system may support remapping),
> although the drive firmware's hardware sector remapping could kick in
> when the drive firmware detects a bad block when it's accessed by the
> file system diagnostic.
> This is why I wonder about Spinrite. While it seems to be an awesome
> program, it DOES pay attention to partition tables and partitions, so
> it's not just checking the raw sectors on the disk. But it checks an
> ext3 partition just as readily as an NTFS partition.
> FWIW, I've never managed to recover a damaged drive with Spinrite.
> Either the drives I checked aren't badly enough damaged, so Spinrite
> indicates they're good, or the drive is so badly damaged that even
> Spinrite can't read it. I've had a drive that banged its heads against
> the backstop, run Spinrite on it for 30 days continuously, and while
> Spinrite marked most of the drive as "Bad" it didn't recover a thing.
I've used disk recovery companies for some of the dead drives I've had to deal with. They actually repair drives by replacing components. I've heard some say they are "labs" that do amazing tricks but I've never experienced that and I'm sceptical.
Once they have the drive fixed they probably run much the same tools as we Linux guys would to recover data. They do say they use their own proprietary stuff, but I imagine some amount of that is marketing.
I've used dd with "noerror" to pull off an image then run tools like sleuth kit to recover corrupt files when a lab only gave me valid files. Sometimes you want the bad files for the scraps of data they have.
I could give a Sleuthkit presentation. I'm not an expert but it would be enough for someone to get started.
John Van Ostrand
Net Direct Inc.
564 Weber St. N. Unit 12, Waterloo, ON N2L 5C6
Ph: 866-883-1172 x5102
Linux Solutions / IBM Hardware
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