[smartmontools-support] smartctl fails but badblocks succeeds

[Nathan Stratton Treadway]

On Sat, Jun 25, 2022 at 09:38:56 -0400, Alex wrote:
> The first one doesn't have all that many hours on it.
> 
> 
>    1. Model Family: Western Digital Caviar Black
>    2. Device Model: WDC WD1502FAEX-007BA0
> 
> 
>    1. Num Test_Description Status Remaining LifeTime(hours)
>    LBA_of_first_error
>    2. # 1 Extended offline Completed: read failure 80% 25420 556876652
> 
> https://pastebin.com/P2uvFxfa
> 
> I've also tried to run badblocks on the area around that bad sector, and
> it's succeeded.

As far as I could see, you didn't include the screen log of the
"badblocks" run -- I don't know if that will actually show us anything
useful, but certainly the exact details of the badblocks invocation
(including command-line options) may be important to understanding why
that isn't detecting the error.

I don't use badblocks myself and don't know off-hand if it bypasses the
OS device cache; if it doesn't, it's possible that it doesn't report any
errors because it's accessing the cache rather than causing an actual
read from the physical disk.

I have only a tiny bit of disk-analysis experience, but I've had some
luck using "dd" with iflag=direct to bypass the cache, thus forcing an
actual read of the drive.  So in your case something like this:

  # DEV=/dev/sdb
  # SECT=$(( 556876652 - 100 ))
  # dd iflag=direct if=$DEV of=/dev/null count=200 skip=$SECT 

(where here I just arbitrarily picked a window of 100 sectors on each
side of the target sector to search through)

Then if there is a hardware-level read error, the exact sector that
failed should show up in your kernel log messges.  

(But note that Linux often uses 8-sector blocks for disk IO, so
sometimes the kernel log messages reflect the start of the read block
that errored out rather than the exact sector which failed.)

							Nathan

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