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[HOW TO] Fix bad sectors on hard drive

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[HOW TO] Fix bad sectors on hard drive

Postby matock » Mon Sep 24, 2018 7:10 pm


I would like to share my experience on how to fix bad sectors on hard drive.

Since few month Disk Doctor reports me SMART and scan errors on 1 of my 2 HDs:

[Disk Doctor] S.M.A.R.T quick scanning of Disk 1 result: test completed but a read element failed.
(--> Current_Pending_Sector = 3)

[Disk] There is a media error on sector 6925388032 of the slot 1 disk!
[Disk Doctor] Badblock scanning of Disk 1 completed, 4 bad blocks found. (4/0/0 errors)

The fact is DD reports errors but doesn't fix them!

As my drives are Western Digital (WD40EFRX, 4TB), I used their diagnostic tool Data LifeGuard Diagnostics to scan and fix the drive.

The tool is only for Windows, so you need a Windows PC with a free SATA port and a SATA cable. Remove the faulty drive from the NAS, connect it into your PC and install the DLG tool.

What I did:
- run a Quick test --> failed
- run an Extended test --> it was very long (10h) and reported bad sectors
- click on Repair button --> done!
- run a Quick test again --> ok now

Now I put back the drive into the NAS:
- the Storage Manager detects and rebuild the drive (for 8h)
- after that I checked the SMART --> ok
- I ran a DD scan --> ok

My disk is doing like a charm now, I hope it will last a few more years!

Similar tools are also proposed by other manufacturers like Seagate SeaTools or Toshiba Storage Diagnostic Tool. I didn't check personally.

I hope it helps some of you.
AS-202T / 2x WD 4To Red
Posts: 23
Joined: Tue Nov 12, 2013 6:38 pm

Re: [HOW TO] Fix bad sectors on hard drive

Postby Antonios » Mon Sep 24, 2018 9:28 pm

Man, magnetic surface defects are not 'fixable', that is unless you open up the HDD and take out the platters and re-surface them, put them back in, etc.

Such defects can be either re-mapped somewhere else on the platter, there are some spare sectors for this purpose, or the magnetic head's read error signal level tolerance can be lowered to a point where the bad sector can be read during some r/w test that is running NOW, but who knows if it can be still read (reliably) after a few days.

None of these 'solutions' actually fixes the defect which remains on the platter at the exact same physical location and, depending on the type of defect, in some cases can also 'spread' somewhat to nearby or not so nearby locations.

Of course, one can just get lucky and initially record some useless file that will never need to be read back at the problematic sector location.

Obviously ymmv.

Just my 2c.
Posts: 82
Joined: Tue Jun 27, 2017 1:05 pm

Re: [HOW TO] Fix bad sectors on hard drive

Postby matock » Tue Sep 25, 2018 5:41 pm

Hi Antonios,

I totally agree, bad sectors cannot be "repaired". But it doesn't mean that the issue cannot be fixed (as long the drive is not physically damaged, of course).

The diag tool just marks the sector as defective into the internal allocation table of the drive, in such a way that sectors are not used anymore. Of course this doesn't prevent from other bad sectors in the future. In that case, if it happens too frequently, this is a sign that the drive is reaching its end-of-life and needs to be replaced. Even a new drive, from factory, comes with bad sectors. The internal firmware just has to know where they are located and not use them.

See ... -about-it/

My 2c more.
AS-202T / 2x WD 4To Red
Posts: 23
Joined: Tue Nov 12, 2013 6:38 pm

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