Reset or recover reallocated sectors?

[Paul Connell]

Let me start by saying I wouldn't trust anything to this drive without significant testing, but I just had an interesting issue. One of the drives in my NAS started reporting reallocated sectors. It stated slowly and then increased to where I could just refresh the SMART data and see the number rising. I shut down the unit, ordered a new drive, replaced the failing one and rebuilt the array, so all is good.

I thought I'd use the failed drive to show my son what the inside of hard drives look like (no doubt everything will be solid state by the time he's in his teens). Upon removing the circuit board from the bottom of the drive, I noticed the contact pads for both the motor and the 18 or so pin data connector were heavily tarnished. I figured I'd give a shot at polishing them up with a pencil eraser and seeing how the drive ran. With clean pads, the reallocated sector count ceased increasing completely.

So that has me wondering if the actual surface of the drive was ever failing, or if the decreased signal between the circuit board and the drive were being interpreted as such. None of the other 4 drives in the NAS report any issues at all.

Is there a way to "un-reallocate" the reallocated sectors? If it's possible, I'd repurpose the drive to non-critical storage and see if any problems return.

Thanks in advance.

 

[Paperdoc]

I know of no way to "un-reallocate" Sectors. The HDD's internal self-diagnostic and fixing routines will replace "faulty" Sectors with known-good ones from its initial stock of spares, but I've never heard of it having any ability to re-examine ones already logged as "Failed" to see if they really could be re-used.

The best I can suggest is that you use a Zero Fill operation on that unit which will certainly wipe out all old data and force the self-diagnostic / fix routines to examine every Sector currently considered "good" and replace any found faulty. When that is done, ALL the Sectors on it that are available for use will be "Good Sectors". Plus, the count of Re-allocated Sectors (that is, the total number of Sectors previously found Faulty and replaced) will be updated. So you can check whether that new total has changed compared to before running the Zero Fill.

At that point you still do NOT know whether the unit really does have hardware problems that will continue to get worse, so I agree it may not be wise to rely on it. IF the only reason for the apparent "faulty" sector rapid development was, in fact, poor electrical contacts, the unit may NOT develop any further Re-allocated Sectors as you use it. BUT it will take some time to keep using it and checking for failure symptoms before you know your answer.

 

[Paul Connell]

Thanks for your reply. So I ended up scanning the drive thoroughly, doing formats that filled the drive with 0's, and no issues were found. Interestingly, the utility I used to read the SMART data in Windows indicated a different reallocated sector count than did the NAS utility.

Since I had the entire NAS backed up to two separate locations, I thought I'd put the drive back in the NAS, let it resync and see what happened. Well, it was a little slower, but the reallocated sector count continued to increase, so the drive is toast in my book. I replaced it with the newly purchased drive and will proceed to dissect the drive for my son's amusement!

One last note, after seeing the significant tarnishing of the pads on the circuit board, I shut the NAS down and removed each of the other drives one at a time, cleaning up those pads. They all had tarnishing, with two almost or as bad as the failed drive. I'm not sure how much, if anything, that had to do with the failed drive, but I figured it couldn't hurt to clean them all up.

 

[Paperdoc]

Thanks for the update. I agree with what you did, and your conclusions. I hope you and your son will enjoy the dissection. One small note - the magnet inside for the head movement arm is VERY strong. So that's interesting, and requires a little care in where you put it.

Come to think of it, this is an intriguing opportunity. By the time your son (depends on his age) is an adult, using today's common HDD may almost be gone!