input/output error on hd
jerrymc at msu.edu
Sun Feb 25 18:23:51 UTC 2007
On Sun, Feb 25, 2007 at 10:38:01AM -0500, Marty Landman wrote:
> On 2/24/07, Jerry McAllister <jerrymc at msu.edu> wrote:
> >Well, I think you are past any label problems now and on to the
> >bad sectors and/or finding superbocks. Although I am not quite clear
> >from above what resulted in the 'INCOMPLETE LABEL...' message.
> Ok then, can you point me to somewhere that can learn about superblocks and
> give me an idea of what to do next?
Most of what I figured out several years ago (and have essentially
forgotten since) came from the handbook and something I found by
searching the web that gave the layout of blocks and chains. I would
have to go back searching again.
> Also assuming my bad sectors really are
> totally bad, wouldn't fsck allow me to mark them as unusable and move on?
No, fsck does not do that. Marking blocks bad happend below the
level of the OS - generally in the disk controller itself. It remaps
sectors until it runs out of spares and when it runs out, it starts
reporting unrecoverable errors. This is not even reported to the OS
until it runs out of spares.
The only thing you can do with those bad sectors is to try and figure
out if any of them are superblocks. If they are, you can probably
rebuild it from other superblock clones. If it is not, it is probably
lost data. In that case try to overwrite the bad sector. If that
works, then the sector itself is OK, but the data that was there is
gone. If it doesn't work, then it is bad and there is a good chance
that more than data got nuked in the power failure - eg, it damaged
the disk or controller in some way.
But, the next thing seems to be learning about how to follow the file
chains and how to find and read and write superblocks. Alternatively
you can decide it isn't worth the effort to recover and try and write
over the drive completely - just totally trash it - and see if those
bad sectors will write. If you did that, then you would have to rebuild
the slice and partition table and do a newfs before you could again
use the drive and everything previously on it would be lost.
Maybe someone who has some experience in tracking file chains can
respond and give you more helpp than can I.
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