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

[Hans Reiser <reiser@namesys.com>]

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