[EdLUG] 4TB HDD showing bad blocks

[Stephen Tweedie]

Hi,

On Wed, 2023-02-15 at 18:04 +0000, Roy wrote:
> Andrew,
> To add to the good stuff said by Stephen, you may coax one more read
> from hard to read sectors with ddrescue.
>  You need to make an image and save the log file, That requires
> another 4Tb of space for the image and some space somewhere else for
> the log.
> Run   smartctl -x   and save the result. Post it if you like.
> Look at the duration for the long test in the output. 
> Use smartctl to run the long test. Everything happens inside the
> drive, so if you have cable or motherboard problems, they will be
> ignored.  Wait as least as long as the long test completion takes.
> Run  smartctl -x  again.
> The key things to look at are how much of the test completed, The
> Pending Sectors and the Reallocated Sector count. 
> The Pending Sector count is the number of sectors that the drive
> would like to remap if only it could read them.
> Running ddrescue in place, or throwing away recovered data is a
> really bad idea. If your drive is on the verge of failing, the time
> to run ddrescue may tip it over the edge. 

True.... but there was no sign in Andrew's initial post that there is
anything wrong with the drive.  Some small number of bad blocks is
routine and expected, and not necessarily a sign of immanent failure.

Drives today run on the very edge of usable density.  They write so
densely that the signal-to-noise ratio on a subsequent read is
horrible: they only read back anything at all by employing massive
amounts of error correction encoding.  That's a good thing — the disk
space used by the ECC is more than outweighed by the space gained by
higher density.

But those densities, and the poor s/n ratio to start with, does mean
that it takes only the tiniest defect to render a single block
unusable.  

Bad blocks are not necessarily a sign of failure, they can just be the
drive working as intended on hardware that is designed to extreme
limits.

The big thing to watch out for is a sudden increase in bad blocks; that
is much more likely to indicate failing hardware.  A few bad blocks
appearing slowly over time is much less worrying.

--Stephen
> 

> On 15/02/2023 03:31, Andrew Smith wrote:
>  
> >  
> > Guys 
> > My 4TB WD SATA HDD has started showing bad blocks.
> > It has SMART.
> > How do I configure it, probably with smartctl, to automatically map
> > the bad blocks when they arise to good ones elsewhere  on the
> > drive?
> > In addition, if I get a list of bad blocks using badblocks, how can
> > I find the names of the files using these ad blocks ?
> > Andrew
> >  
> >  
>  

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