Re: Trouble finding bad block on WDC WD1600SB-01KBA0

On 11-Jan-2017 12:58, Carlos E. R. wrote:
> If this happens during a write, the sector is reallocated. If it 
> happens
> during a read, reallocation is postponed and the sector noted. I don't
> know if it creates a list and how to read that list.

Subsequent reads - of the whole disk, did not log any errors,  nor did 
they clear the "current pending sector" count.  That's the odd part - 
the disk had somewhere stored "there is some problem with block N" and 
incremented the pending sector count, but it seems that several reads 
from block N (wherever that was) which completed without error were not 
enough to change its mind.

It seems like a major shortcoming in the SMART protocol that there is no 
"list the pending sectors" command.  The disk must have this 
information, otherwise we cannot explain the way it behaved in this 
case.

> 
> Reallocation happens during an attempted write, to another permanent
> location.

Agreed.

> 
> I don't know what happened during the badblock run, because it is a 
> read
> operation.

with -nvs there is also a write after the read.  It presumably read the 
iffy block successfully (for about the 6th time) and when it wrote it 
back the flag finally cleared.  It may or may not have been reallocated, 
but if it was, the counter did not increment.  It seems about as likely 
that the disk just cleared the flag.  Perhaps the firmware at that point 
did a couple of read/write tests on its own and decided all was now OK.  
We can't really know what the disk does "underneath" the level we 
interact with.

Regards,

David Mathog
[email protected]
Manager, Sequence Analysis Facility, Biology Division, Caltech

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