Re: Why are bad disk sectors numbered strangely, and what happens to them?

[John Bradford]

Quote from "Norman Diamond" <ndiamond@xxxxxxxxxxxxx>:
> John Bradford replied to me:
> 
> > > > > How can I tell Linux to read every sector in the partition?  Oh, I
> > > > > might know this one,
> > > > >   dd if=/dev/hda8 of=/dev/null
> > > > > I want to make sure that the drive is now using a non-defective
> > > > > replacement sector.
> > > >
> > > > A read won't necessarily do that.  You might have to write to a
> > > > defective sector to force re-allocation.
> > >
> > > I agree, we are not sure if a read will do that.  That is the reason why
> > > two of my preceding questions were:
> > >
> > >    How can I find out which file contains the bad sector?  I would like
> > >    to try to recreate the file from a source of good data.
> >
> > How are you going to make sure you write it in the same location as it was
> > before?
> 
> Mostly it doesn't matter.  The primary purpose of this bit of it is to
> recreate the file to contain good data, which is why I would try to recreate
> it from a source of good data.

OK.

>  The secondary purpose is:
>   IF the bad sector doesn't get reused then great, then the next bit of
> effort will be to try to get the sector marked as bad, if there is any way
> to do that under Linux.  See the next question, which is now being reposted
> for at least the fourth time.
>   BUT IF the same sector number gets rewritten then hopefully the same
> sector number will be associated with a reallocated non-defective sector and
> the data will get written properly.

Yes, that's what I'd hope, unless the disk ran out of spare space to
allocate.

> > >    How can I tell Linux to mark the sector as bad, knowing the LBA
> > >    sector number?
> >
> > Don't.  If the drive can't fix this problem itself, throw it in the bin.
> 
> THE DRIVE HAS 1, ONE, HITOTSU, UNO, UN, BAD SECTOR.

No, the last SMART test re-allocated one sector.  That sector may have
gone bad in the next few minutes.  Unlikely, but possible.

>  The drive is capable of
> doing reallocations.  What kind of operation can be done that will persuade
> the drive to do the reallocation?

The drive has _done_ a reallocation.  You posted that the reallocated
sector count had gone from 1 to 2.  This is why I said if it can't fix
the problem, bin it.  It doesn't seem to have fixed the problem yet.

> > > And that is also the reason why my last question, which Mr. Bradford
> > > replied to, had the stated purpose of making sure that the drive is now
> > > using a non-defective replacement sector after the preceding operations
> > > have been carried out.
> >
> > Backup your data.
> 
> I want to fix the defective file from an existing backup or recomputation.
> Aside from that, it is my crash box (as already posted in this thread).

Somebody else might read this thread, and want full instructions.  It
might be your crash box, but somebody else might have data they want
to preserve.

>  The
> questions are still important because sometimes this kind of thing happens
> on machines that aren't crash boxes, and it is not customary to dump a drive
> when 99.99% of its preparations for error recovery are still intact.
> 
> > Run the S.M.A.R.T. tests.
> 
> I DID.  YOU REPLIED TO MY POSTING WHERE I REPORTED THEM.

1. I know.  I read your original post
2. I am providing instructions that other people might follow in the
   future, that is why I am making sure they are complete.
3. Run the tests again.  Your drive fixed one bad sector, let's see if
   it completes the test again without finding more.

John.
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