Re: Blockbusting news, this is important (Re: Why are bad disk sectorsnumbered strangely, and what happens to them?)

[Hans Reiser]

Norman Diamond wrote:

> Replying first to Hans Reiser; below to Russell King and Pavel Machek.
>
>  
>
> > Instead of recording the bad blocks, just write to them.
> >    
>
> If writes are guaranteed to force reallocations then this is potentially
> part of a solution.
>
> I still remain suspicious because the first failed read was milliseconds or
> minutes after the preceding write.  I think the odds are very high that the
> sector was already bad at the time of the write but reallocation did not
> occur.  It is possible but I think very unlikely that the sector was
> reallocated to a different physical sector which went bad milliseconds after
> being written after reallocation, and equally unlikely that the sector
> wasn't reallocated because it really hadn't been bad but went bad
> milliseconds later.  In other words, I think it is overwhelmingly likely
> that the write failed but was not detected as such and did not result in
> reallocation.
>  
perform the write after the failed read, that way the drive knows it is 
a bad block at the time you write.

> Now, maybe there is a technique to force it anyway.  When a partition is
> newly created and is being formatted with the intention of writing data a
> few minutes later, do writes that "should" have a better chance of being
> detected.  The way to start this is to simply write every block, but this is
> obviously insufficient because my block did get written shortly after the
> partition was formatted and that write didn't cause the block to be
> reallocated.  So in addition to simply writing every block, also read every
> block.  For each read that fails, proceed to do another write which "should"
> force reallocation.
>
> Mr. Reiser, when I created a partition of your design, that technique was
> not offered.  Why?  And will it soon start being offered?
>  
I think I discussed with Vitaly offering users the option of writing, 
reading, and then writing again, every block before mkreiserfs.  I 
forget what happened to that idea, Vitaly?

> Also, I remain highly suspicious that for each read that fails, when the
> formatting program proceeds to do another write which "should" force
> reallocation, the drive might not do it.
I am not going to worry about such suspicions without evidence or drive 
manufacturer comment, as it has not been our experience so far.

> Why does it matter?  The drive already reported a read failure.  Maybe Linux
> programs aren't all smart enough to inform the user when a read operation
> results in an I/O error, but drivers could be smarter.
There is a general problem with reporting urgent kernel messages to 
users thanks to GUIs covering over the console.



--
Hans


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